Now you would have to have seen a recent episode of "Angel" to know what I am talking about, but the men all became brutes. Wesley, sweet, shy, Wesley was no exception to the rule. He showed his dark self up fully. He was mean verbally and physically abusive. That had nothing to do with not having a soul. It made something, primal rise to the surface, and I hate to say it, but I think that was a true depiction of who Wesley could be. yet it's a side he fully chooses to push down, and keeps very latent. A vampire Wesley would be free of that and he could do all the carnage he liked, and no conscience headache the next day.
I could go on and on with this subject, but I think a soul is something they all have. How else could they retain any semblance of the persons they use to be, likes dislikes, a lot of that stays. Conscience is a choice, as is really bad behavior. The need to drink blood for the vampire is not a choice. What's latent rises to the surface, when you are a vamp, and conscience gets pushed down into this hidden place. A lot of people go through life like this, but there are the few, who do not do this. If they changed to vampires we would see a lot of the same, because the latent is already showning on the surface.
Spike Quotes.
Spike tells Angel and Buffy about love in Lovers Walk:
"You're not friends. You'll never be friends. You'll be in love till it kills you both. You'll fight, and you'll shag, and you'll hate each other till it makes you quiver, but you'll never be friends. Love isn't brains children, it's blood. Blood screaming inside you to work it's will."
Quote 2."I may be love's bitch, but at least I'm man enough to admit it."