And the thing about Xander wanting to kill Angel in the beginnig and not killing Anya now isn´t much of a stretch. First of all he loves Anya which cloudes his judgement. But on the other hand, now he has seen that you can rescue people who has gone bad. Angel, Willow, Spike (?). So why not try to rescue Anya too?
I agree that it became far more complicated with Xander and Buffy later on. I've seen some fans accuse Buffy of being hypocritical because she couldn't kill Angelus straight away, but I disagree. She's simply grown. She saw what damage resulted in allowing Angelus to remain alive because of her feelings, she wasn't going to make that same mistake again. And she shouldn't, she was right, Anya chose to become a demon *twice* and had just murdered twelve people. She's the slayer, she would have been irresponsible to not go after Anya.
But I'm glad Xander finally got to feel a little of what Buffy was feeling when Angel lost his soul. Because it's something he'd never really dealt with well concerning Buffy, and something he hadn't had to experience until it happened to him.
And Xanders biggest problem with Angel wasn´t that he was a vampire (my opinion), he was simply jealous. Angel being a vampire just made it 1000 times worse and gave a "better" reason. And can you truly blame him för not liking vampires? Just found out they existed and knowing of Angelus past?
I agree that jealousy played a big part in it, but I do think being a vampire made his hatred a lot worse. I've never enjoyed Xander hating Angel because he's a vampire. At first, sure. They didn't know the full story and it's perfectly within a character's rights to hate vampires, the show proved a point of how stupid the people were in 'Lie to Me' for pretending vampires were something they were not. They're killers, they deserve the hate. But after the gang found out about Angel's soul I felt Xander's hatred was unwarranted. He even states I 'Passion' that he desveres a little something for not saying "I told you so" in regards to Angel, which always worried me a little. If he honestly can't differentiate between Angel and Angelus, there's a big problem there. He never really understood Angel's character.