I wanted to add that while I do think fans need to be consistent in judging both vampires, for Buffy and friends, their very interactions with both vampires was inherently inconsistent, which leads to quite a lot of points to be taken into consideration.
Remember that on behalf of the scoobies, the specific judgment Spike receives post chip in response to what he's done while soulless for the last 100 years is largely due to his position in-- or near-- the scooby circle. For Buffy and friends, before the chip, Spike was judged just as Angelus had been judged; he was simply a soulless vampire that needed to be killed. After the chip was implanted, he was seen in the same light but as he was defenseless, they began to take on a neutral attitude toward him. Throughout season 4, they (unintentionally and often unknowingly) began to develop a relationship with him and actually depended on him for information, correctly assuming that his need to survive would be enough motivation for him to help them. Of course once they discovered that he was playing both sides for a little while, that temporarily symbiotic relationship was called into question, at which point he truly surprised them by helping them in the final battle.
Because of that, in the start of season 5, their stance on Spike is basically back to neutral, but slowly and surely they start to depend on him once again. Riley wants information on Dracula. The gang needs more muscle. Soon they are, however reluctantly and unwittingly, developing a relationship with Spike once again. Then, of course, he reveals Riley's betrayal. With Riley out of the picture, Buffy is even more dependent upon Spike for muscle. For information. By the end of the season of course, he is a scooby for all intents and purposes. He is literally sacrificing his life to save them, (Intervention, Spiral, Weight of the World, the Gift), regardless of the debatable nature of his motivation.
From this point forward, Spike is a trusted, if not universally liked, contact. In Buffy's absence, it is assumed on a nightly basis that he will patrol with them, save them from demons, and protect Dawn.
So now, the very same creature with the very same composition as the one who came to Sunnydale to kill Buffy all those years ago, is being relied upon to not only refrain from killing, but to actively help the mission and save the scoobies. This is completely different from the scenario with Angel. It was always Angel who was the (sometimes reluctantly) trusted and accepted go-to vampire. It was always Angelus who was feared and targeted. Of course it was much easier for Buffy and friends to separate Angel and Angelus; he made that quite simple for them. The writers helped by making it so that Angel conveniently forgot some of his most recent and atrocious deeds upon being re-cursed in "Becoming II." It was all so black and white: "here is your hero, here is your demon."
But for Spike? Once the series of events had been put into motion that would act as a form of behavior modification, he couldn't be looked upon in the same light as he was while enemy to the gang; the series of events listed above demonstrate that this is the case.
When the scoobies exhibited disappointment and disbelief toward a late season, soulless Spike, those feelings were emotionally driven, and based upon their conflicting, positive interactions with him. Indeed by the events of Seeing Red, Spike's unfavorable actions are no longer expected from him and he is in fact held to the same standards as any one of the ensouled scoobies. As, well, Buffy's lover. They hold him accountable for his actions because they've seen him be good. Of course, it is due to the progress that Spike had made that he did not successfully rape Buffy--didn't try harder, and decided he couldn't trust himself to exist in her presence without a soul. Spike holds himself to these same standards, which is exactly why he goes to Africa.
Once again, Spike is the un-dead embodiment of "grey area." For me, I can keep my judgments consistent between vampires, throughout both souled and soulless existence, because for me, there is a difference between soulless Spike and soulless chipped Spike on the path to redemption. Here's what I mean:
Angelus and pre season 4 Spike for me are the same. As accountable for their actions as naturally predatory animals or the mentally ill are for theirs. Once the inherent humanity in Spike is allowed to come through after the implementation of the chip and the subsequent realization of feelings for a human hero, and once the notions of empathy and sacrifice make their way back in his favor, (by season 6 when he is truly exhibiting the aforementioned qualities), I begin to hold him accountable for all of his present and future actions the same way I do other scoobies. The same way they do. By season 6 Spike's not a monster and he's not yet a man. He's not evil Angelus and he's not wholly good Angel. He's something completely different, altogether, and that needs to be taken into account when you compare a soulless Spike to Angelus.
This is exactly what Spike realizes, and is why he gets his soul.
I hope all of that made some sense.
