In this essay, Erma Petrova argues that, whereas the first seasons of Buffy focused on external threats that sought to corrupt the order of the world, the later seasons shifted the threat towards the internal – the result being that the show’s main characters embraced a side of themselves that was also evil, irrational, or dangerous. The Slayer is the one who must maintain the difference between good and evil and makes sure that good doesn’t become evil. At the same time, she is the most ambiguous one, the one who is ready to cut all ties with family and friends and kill people she loves, if necessary. The requirement that she know exactly which side she must stay on (regardless of where those she loves are) gives her the responsibility to keep the other “other” at all costs even at the cost of becoming an “other” herself. Paradoxically, she protects the line that separates good from evil by crossing it and by becoming more and more “other.”
While the first seasons of Buffy are structured around an external threat seeking to corrupt the order of the world, later the source of the threat becomes increasingly internal, and the characters must embrace a side of themselves which is evil, irrational, or dangerous. When Giles kills an arguably innocent Ben, he does not suffer the moral ambiguity that Willow encounters when she kills a guilty Warren. Willow has to deal with an evil internal to her in a way Giles does not, and this apparent discrepancy is the result of a general evolution of the series, rather than a double standard.
The murder f Ben is comparable to the murder of Warren, even though Ben is mostly innocent and Warren is mostly guilty. They are both human, and their deaths are necessary to stop further evil. Even though Ben cohabits the same body with the hell god Glory, he, as an independent being, is innocent of Glory’s actions, as the Scoobies uniformly agree: “What about Ben? He can be killed, right? I mean, I know he’s an innocent, but, you know, not, like ‘Dawn’ innocent. We could kill… a regular guy… (no we couldn’t) God.” Even the script directions (“no we couldn’t”) suggest that the way Xander delivers these lines should emphasize the moral impossibility of killing Ben as a way of stopping Glory. Being Glory is to Ben what being the Key is to Dawn: it could make him “other” but it cannot make him either good or bad on Glory’s behalf. It is true that Ben is guilty of other things — he summons the demon who kills (or merely finishes off) Glory’s brain sucked victims; and, in “Listening to Fear,” there is even a real chance that Joyce might get killed because of him (an event which Buffy prevents from happening).
It is also true that Ben betrays Dawn and humanity in general by selling his soul to Glory and agreeing to help her in exchange for his life (or, rather, his immortality). But the Scooby gang doesn’t know about any of these things and, even though Dawn obviously knows that Ben is a weak and, by virtue of the circumstances, treacherous human being because of his weakness, Giles certainly has no knowledge of any of Ben’s immoral actions when he kills him. Giles is acting on the assumption that Ben is completely innocent but powerless to stop Glory, should she ever wish to return for purposes of payback. Giles realizes that something needs to be done and that whoever does it will be incurring feelings of guilt — otherwise he would have left Buffy to do it. By saving her from the act of murder, Giles acknowledges the moral ambiguity of the act itself, the (apparent) innocence of Ben, and the inevitability of guilt for whoever happens to do what, in Giles’ view, has to be done. (Similarly, he would have killed Dawn, if he had to). But, we notice, feelings of guilt never come, and the ambiguity of this act never surfaces (script directions describe Giles during/after the murder this way: “Giles’ expression never changes”). Giles objectifies the evil — it is not in him, but he is merely the carrier, the means for an act which must be done, one way or another.
In contrast, when Willow kills Warren, a situation uncannily similar (i.e., a Scooby killing a human) results in entirely different moral consequences. Warren also, presumably, deserves to be killed, and, one way or another, somebody will have to do it. But the series makes sure we understand that there are restrictions to who can do it and that Willow is not morally eligible for it. In the case of Ben, anyone could be allowed to kill him (if we agree that he has to be killed), and the only requirement is that the “killer” is in fact physically capable of doing it and ready to take the responsibility for the act (similarly, when Giles realizes that Dawn may have to be killed, he knows that he cannot physically do it (because either Glory or Buffy would stop him), so he appeals to Buffy to see what has to be done). In the case of Warren, on the other hand, even though Willow is more than willing to take the responsibility and to perform the act (with great creativity), this is not enough anymore.
She needs a different kind of authority, the authority of not having chosen this solution. If the murder had been forced on her as the only way to protect Tara (and in time to protect her), then Willow would have had the right to take a life. In the case of Ben, Giles is aware of the fact that there is no one else to kill him (the police are not capable to grasping the danger he represents, and Buffy is not ready to take the responsibility). In the case of Warren, there are multiple options for killing and/or arresting the “bad guy,” and Willow is not in a situation (e.g., self-defense) which compels her to do it herself. We are shown that, if other options are available, one should not take the responsibility for violence oneself. And the series presents us more and more often with situations where other options are in fact available, which places on the shoulders of the characters the responsibility not to choose them; e.g., Willow has the option to kill or not to kill Warren; Buffy, in her dream vision of the mental hospital in “Normal Again,” has the option to kill or not kill her friends (both options seem acceptable to her), and even Spike, who can hardly be said to have any choice at all in the matter, somehow manages to discover more than one option (soul or not soul).
Multiple options in themselves are initially seen as a good thing: while “The Gift” begins with the grim prospect of Buffy either killing Dawn or destroying humanity, the gang works together to find another solution, and by the end of the episode new options have been found, foreshadowing both the availability of multiple choices without a right answer (both killing Dawn to save humanity and letting humanity be destroyed by not killing Dawn can seem like the right choice), and the self destructive solutions which all of the characters will eventually choose in season six (beginning with Buffy giving up her life at the very end of season five — an option that was not the preferred or even foreseen result of the search for new options, options which everyone was desperate to find).
While the series doesn’t really give us any choice in Giles’ murder of Ben, it increasingly centres on the complexity of situations where a choice is waiting to be made, and it is not immediately clear which course of action is the right one. In the case of Willow, it is conceivable to say that the action she chooses (killing Warren) is the right one, but there is something wrong about her being the one to choose it, or about this murder being a matter of choice at all. There is a sense in which the murder could only be justified if there weren’t any other options to choose from. (If the Slayer kills demons, it’s because no one else can; we could even say that the Slayer is the name for not having any other choice but to kill, which is what upgrades the killing to “slaying”; a Slayer would not be possible in a world where the normal human authorities are capable of doing her job.)
After working so hard to increase the number of options available to them, the characters still end up choosing the most self destructive one. The expansion of the range of available choices puts the emphasis on the character who has to choose. We don’t know what the character will do. The good is not That Which Buffy Chooses, and the bad is not always that which Buffy fights. It is no longer the case that the character will necessarily choose the right action: the moment the right action becomes a matter of choice, it is no longer something that “always” happens.
The measure of good and evil in Buffy is choice. We cannot say that Giles is evil when he kills Ben, because he doesn’t seem to have any choice about it. Choice is the difference between Buffy’s attitude toward Dawn when we first meet Dawn (Joyce has to force Buffy to take care of her sister: "Buffy? If you’re going out, why don’t you take you sister with you?” [“Buffy vs. Dracula”]), and Buffy warning everyone that she will take care of Dawn no matter what (“I’ll kill anyone who comes near Dawn” [“The Gift”]). In any other hero narrative, Buffy would have been faced with a situation where she must save Dawn at all costs, and her heroism would come from her determination to do what she has to do (cf. Giles and Ben); in other words, she would have no choice but to save Dawn.
In Buffy the Vampire Slayer, however, this is not enough to make a “good guy,” and the heroine is in fact faced with the opposite situation: she does not have a choice but to kill Dawn in order to save the world, but, even though she is not given any other options, somehow she manages to choose an other option. In other words, while the standard hero does what he must, Buffy does what seems the right thing to do even if this is not available as an option at all and all the options are “wrong”:
Significantly, none of Buffy’s friends, including her boyfriend Riley, can distinguish between the two; it is conceivable to the characters that Buffy might behave like Faith in “Who Are You” because she did behave like Faith in "Bad Girls.” The recognition that there is something wrong with Buffy in “Who Are You” comes in fact from an outsider, Tara, who hasn’t even met Buffy before. This suggests that there is something objectively wrong with Buffy’s occupying another body in general, but not that there is something wrong about Buffy being Faith, specifically; or, more precisely, the fact that Faith-in-Buffy-body is different from both Faith and Buffy (in that her spiritual aura doesn’t match her body) is not proof that Buffy-in-one-piece is essentially different from Faith in one piece or at least the Scoobies cannot distinguish between them, and what Tara is able to distinguish is someone in one piece from someone not in one piece, but not Buffy from Faith. Tara’s detection of the body/spirit discrepancy does not mean that either Buffy or Faith is “bad,” but that there is something Frankenstein-like and wrong about mixing their body and soul parts. But this doesn’t mean that Faith in Buffy-body is noticeably “worse” than Buffy, or that Buffy in Faith-body is noticeably “better” than Faith (in fact, Buffy-in-Faith-body lays quite a few punches on people in order to escape from the Council bloodhounds in “Who Are You,” just as Faith kicks some butt in her escape from Wesley and his attendant Council muscle in “Consequences”).
If we take Buffy’s susceptibility to Dracula’s hypnosis as symbolic of her inability to distinguish between good and evil (she does not recognize Dracula as evil while she is under his influence), her taste of evil opens her eyes to this distinction. The forbidden knowledge is a knowledge that allows her to be good without being innocent, to choose good while also knowing that she is equally able to choose evil; in other words, being good is defined as having the ability to choose evil and yet not choosing it. To choose evil before tasting it would be impossible (because this would not be a real choice); both choosing evil and rejecting evil require the taste of evil. (This goes for Willow’s destructive magic as well: in her case, being good without being innocent means learning to control the magic she knows she has (season seven), rather than avoiding magic at all costs (season six); it would be impossible to distinguish between good magic and evil magic by avoiding all magic.) 
The development of Spike is also based on the increasing (and constantly sought) possibility of choice: the chip does not exactly leave him without a choice to be bad (as we saw in “The Yoko Factor,” he can do a lot of damage by using his brain rather than his fangs), yet the chip introduces, however subtly, the additional possibility of being good. However, Spike is able to see the “good” side even before the chip, for example in his reaction to Kendra’s death in “Becoming,” part 2: “SPIKE (genuinely proud): Dru bagged a slayer? She didn’t tell me! Good for her! (off Buffy’s look) Well, not from your perspective, I suppose…” 
If the dark side is defined as the “other” side (dark by virtue of being other), we see that the characters gradually become more what they’re not, recognizing and claiming their respective “others,” rather than renouncing them. We know, of course, that to be good Spike must not be forced into it (just as, to be evil, Giles must kill without being forced to and for purposes other than saving the world). We know that Buffy refuses to recognize the lack of choice when she is told to kill Dawn — it is made clear to us that she must save the world/kill Dawn because she is “good,” but she refuses to be “good” at this price and publicly apologizes to her friends for letting them die: “I’m sorry. I love you all, but I’m sorry” (“The Gift”). Much like Buffy, Spike refuses to recognize that he is cornered in a similar way — in his case, trapped into being evil. 
The self-awareness, the need to claim responsibility for both the good and the "less good” (“Smashed”) actions, is a need which goes beyond that of the slayer as such. Buffy would have been able to do her job very well without bothering to know why she does what she does; the only thing she really needs to know is how to kill. When Faith is temporarily “good” in imitation of Buffy, she can do what is right without exactly knowing why, for the simple reason that “good” is occasionally fashionable, easier, or temporarily useful for some other purpose. If Faith had continued this way, there is no reason to suspect that she would not have been a good slayer. The slayer, seen as a tool, a “killer,” is not expected to overdo the self-awareness bit. But Buffy surpasses all traditional definitions of the council and other slayers and watchers about what a slayer should be: “The slayer doesn’t walk in the world…. No… friends… just the kill… we are… alone” (“Restless”). It is safe to say that she is not what anyone would have suspected, and she may very well be the one to introduce the definition of “slayer” as different from “killer.” (BUFFY: “I prefer the term ‘Slayer.’ ‘Killer’ just sounds so…” DRACULA: “Naked?”).