I'm 100% for a dog's license for any breed and particular for potentially dangerous breeds.
If you think though, that a Pitbull (or any other dog really) snaps suddenly and without reason, you don't know your shit.
Punishment, especially physical one and teaching (often with physical punishment) your dog not to growl when there's something he doesn't like (for example getting pet by strangers) is how most people still raise their dogs and it's a "fantastic" recipe to get your dog to snap "for no reason".
Pits don't snap for no reason. They are just genetically predisposed to attacking other animals. The warning signs are there if you know what to look for.
And yeah, positive reinforcement training is the way to go.
Problem is, most dog owners are lazy as fuck
Pits require, without missing a day, an hour and a half to 2 hours a day of HARD exercise. Terriers are a high energy breed. Not a walk around the block twice a day. I mean running full out, exhausting exercise. Owners who do not commit to making sure they get their their 2 hours a day exercise(Which is most owners) are creating a future problem. These dogs get neurotic when they don't get that exercise.
So yeah, if you work at 9AM to 5pm, you must then put aside 2 hours of that day of your personal time to ensuring the terrier gets its exercise. How many folks do you know who will do that and not just bitch out and say "A walk around the block is enough!"? Every day for the rest of the dog's life you must do that. You can't be too tired, too sick , too busy or just want to take a day off. EVERY DAY its required.
People get dogs and neglect the dog's needs. When it's a Lab these negative reactions are a bother and they tear up furniture, but when it's a power breed those negative reactions can be fatal.
A 20 year old hipster who weighs 90 lbs and can't hold a pit Bull back when it decides to go is a very dangerous thing. Especially since they are usually caught off guard by it. They raise it from the time its a puppy and socialize it somewhat and are convinced they can be trained to never fight other dogs. Or they think because it was submissive as a puppy around other dogs that it means they will be like that forever. Then the dog reaches adolescence and its personality undergoes an overhaul and "catches them by surprise" one day when it attacks another dog without signalling.
And they are usually terrible Pit Bull owners. Honestly an alpha trashy muscle dude can at least control his dog.
Spreading the gospel that a pit is a gentle animal for a lazy family that won't train or exercise it or be responsible owners is nearly just as bad as a ghetto dirtbag owner. If you do that with a Lab, the results are almost always still safe, aside from some destroyed furniture and the occasional puncture wound. With a pit, it is dangerous. To your property and especially to other dogs or cats around it can get to.
But people get these silly assumptions that a "bad owner" means you beat the dog and train it to attack" when they don't realize neglect and laziness make you JUST AS BAD a pit owner.