Hey--I agree with you that it's bad worldbuilding and that it would have been way more interesting had he done otherwise. But he had no idea that there would be any exceptions to his rule other than Angel when he first started writing S1, so by the time he gets to Spike and Clem and others (and I've never seen Clem as "good," only as "harmless"--he eats kittens! ;p ), he's already laid down these rules that he can't violate. It's writing himself into a corner, sure, but he clearly didn't he'd be writing for five or six or seven seasons.

You think Anya had a soul while she was a vengeance demon? I need to rewatch that one, then! I always thought she had one as a human, then lost it, then regained it when she became human again, but I could easily be missing something.

Honestly, I don't think that the two readings are that far apart. Having a soul doesn't make you good or ensure that you will be (see: Warren, Angel in AtS S2, etc.), but it gives you the capacity to be good (by giving you guilt, compassion, a conscience, etc.) that you can't have outside of it--not, like Clem, just "not bad" but actively good if you choose to be--and gives you the ability to be selfless, which is the key component for love.

I adore Dawn, and I do love the idea of letting her be the world-saver.