I believe that Joss saw the character of Spike as the perfect way to show Buffy, the Scoobies, and the audience that there can be evil out there that isn't completely evil, it's all shades of gray. Of course, he also used other characters to show the other side of the spectrum, that even good isn't always completely good (this is apparent in Buffy, Giles, and let's not forget, Faith). Spike's chip was a place-holder, to an extent, for where his soul should be. He was forced to bring no harm to anything "good," which even included Buffy for a while. With that in mind, why is it that chipped-Spike still hung around? Sure, the chip kept him from hurting good things, but it didn't force him to pal around with the good guys, especially after Buffy died. Why would anybody who was generally shunned by a group of people stay around to help them? I think it's quite clear that it was because he cared for Buffy enough that he would continue to help the people that she loved even with her gone and even though they didn't like him overly much. This isn't something one might observe in other "evil" demons. I agree that Spike was very obsessive over Buffy, but if that's all he was, obsessed, then wouldn't he leave the gang after Buffy died? After all, she was gone, dead, he had no idea about Willow's plan to resurrect her, and yet he stayed. This sort of sentiment was also seen when Glory was torturing him for information. As we all know, Spike didn't tell her anything because he knew that if he did, it would bring harm to Buffy and Dawn. If that is just plain obsession, then WOW... I mean, I've had plenty of obsessions in my life, but let me tell you, I'd never die for Harry Potter. The only emotion or feeling that we as human beings understand that could bring out such loyalty is love. It doesn't have to be love love. Giles would have done the same for Buffy, and I think it's safe to say that his love for her was purely platonic. Spike's love, as we know, was not platonic, but a fiery, passionate, romantic one.
The passion in his love, mixed in with the part about him not having a soul (and also able to hurt Buffy at this point) led to the attempted rape. This sort of thing, sadly, happens everyday and from what I've heard, the act of committing it doesn't necessarily mean that the attacker is soulless. If anything, it breaks up one's soul, never to be whole again. However, Spike's lack of a soul at this crucial moment did not separate him from the agony and yes, remorse, that he felt for the pain he caused Buffy. Humans deal with remorse and guilt in different ways, and I suspect that it is quite possible for demons to as well. After all, vampires still retain a little bit of the essence of their human-selves (as seen in vamp-Willow and her tendency towards women). When Spike became a vampire, he became what he always wanted to be... the right amount of fighter and lover. To further the point, when Angel became a vampire, one of the first things he did was kill his father. Afterward, he went on to being the killing-machine that he was until his soul was restored. Spike's first thought after he became a vampire was to, yes, kill his mother, but only to save her from what he thought was worse, death. This, I think, shows a fundamental difference between two inherently evil vampires who both eventually had their souls returned to them. So does that mean that soulless Spike was more capable to love, to feel remorse, do what other vampires couldn't do? My answer? Shades of gray...
