All dogs can potentially cause harm, banning certain breeds imo would't work. They should however make it harder to get a dog. Go to a class, take some form of aptitude test and based on those results plus what you need the dog for you are allowed certain dogs. It would stop people getting dogs when they don't want them as well. And all dogs should have to be on a lead, I'm sick of people letting there dog run at mine and have no control to get it back.