Try to explain to a 2 year old why my completely harmless Shi-poo bit her. Your logic makes no sense in the real world. Even adults will reach for a stranger's dog even if they own 5,000 large dogs because their dogs are sweet.

My 8 year old shi-poo, that weighs under 7 lbs is as chill as a cat. All she does all day is sleep and give kisses. Never once has she bitten or even threatened to bite. But someone's 1-2 year old decided to start fucking around with my dog by grabbing her tail and pulling. My dog warned her. The kid then decided to pull on her ear and my dog snapped at her and the kid ran away. Try teaching that kid how to properly handle a dog with parents who never owned a dog. Now imagine if my dog was a pitbull, the kid's arm would be ripped from it's socket and used as a chew toy. Or even a slightly bigger dog like my 30lb puggle. He is just as sweet as my shi-poo but even when playing, his bite is significantly stronger, enough to break skin while wrapped in a thick blanket while playing with him.

That doesn't mean people shouldn't have large dogs, it just means if you have small children, they can't defend themselves or handle the kind of damage even a small dog can inflict from a misunderstanding. Dogs aren't machines, they bite if they feel like it and kill if they decide it's necessary. The difference is I can handle a full powered bit on my arm from a pitbull and fight back. Someone who's smaller than me, like a child, will have their entire arm crushed to splinters from that same bite. And children don't exactly know how to handle a situation like that. They'll run and scream, further instigating the dog's attack instead of standing their ground and intimidating the dog enough to force a submission or fight back until the dog submits.