Surely being ostracised by most of a community, which is the eventual result of being an asshat, has more of an effect on someone than some silly negative reputation points, I would think.Surely reaching a certain amount of negative reputation would lead to a eureka moment, when they realise what a pest they are. And we all know you have to acknowledge you have a problem before you can attempt to fix the problem.
The ones that have some hope of rehabilitation are the ones that we are trying to positively reinforce. There's little hope for the ones that have bigger issues.
EDIT: We did come up with plans for a downvote modification, that would cause your post to disappear if enough people downvoted it. That would be an interesting experiment.