Interesting. I never really thought of that.
It's the sort of thing that would happen if, say, someone incapable of love gained the capacity and then was able to look back and realise all they felt was obsession.
I really can't see anyone's view of the benefits of a vampire having a soul, the prisons all over this world have countless mass murderers in them, mass murderers who have a soul.
How many vampire mass murderers are there?
Souls in the Buffyverse are made overly important, especially when it comes to Spike. Mere possession of a soul does not make someone good. Amy's mother, the Zookeeper, the swim coach, the school nurse, Gwendolyn Post, the school cook, the Trio, Caleb, even the Mayor at one point all had souls and it didn't make them good, and there are more.
What a soul seems to do is give someone the potential to be good. It doesn't make them that way. It seems to be more the equivalent of a conscience that may or may not be listened to.
Giving Spike a soul and leaving him on the show was a terrible writing decision. With Angel, Angel had a soul for nearly a century, and we were able to see his struggles over that period. With Spike, the need to have him around and functional meant they couldn't show any struggle for him. No decades of remorse and wandering; instead we got zero remorse and a rapidly functional Spike.
If redeeming a vampire was as easy as giving them a soul, then this makes the Scoobies look bad. Once it was found out how to stick a soul back into Angel, the Scoobies should have done more research and gone around sticking souls into vampires left, right and centre if that was all it took to make them good.