If Pit Bulls are banned I doubt the irresponsible owners of them will rush out to buy Chihuhuas, Yorkies, and such. I see them getting other large dogs that can be a lethal danger. That is why I say it is not about the breed but the owner.
I do think people should think about breed traits carefully before getting any dog. My daughter had neighbors with a border collie- the neighbors neglected the dog and it barked all the time and destroyed their property. The wife told my daughter the dog was getting agressive and she worried about it around her kids and wanted to give it away. My daughter brought it to a rancher friend of ours and he thinks this "horrible" dog is the best dog he ever owned. The dog is now cared for and gets the exercise it needed and it is doing great- doesn't bark, destroy things, and is not ever aggressive. The dog was bred to work livestock and that is what it gets to do now. Every breed has different needs and people need to consider that. Most don't though- most want whatever is popular in their area.