the large proliferation of pit bulls and other aggressive and large dogs is a classic case of unintended consequences with collateral damage from idiotic poorly thought out policies that end up having the opposite effect as intended.
i was lucky enough to live much of my life before universal leash laws.
in Btown, i think the guideline was 35 lbs and under, other than aggressive breeds like a pit, and your dog could run freely and not be a prisoner their entire life.
so the overwhelming vast majority of dog owners just went with smaller dogs and non aggressive breeds, so they could just let their dog out the front door when it had to go or just wanted to go outside.
almost no one owned pits then, because people didn't want the 100 times greater hassle of dog ownership if you had a large dog or aggressive breed.
you had only a small fraction of serious dog/man altercations then, because people who didn't have fenced in yards didn't get large dogs or aggressive breeds, for the obvious reason that dog ownership was 100 times easier if you didn't have to walk your dog X times a day even when it's 5 degrees out, and life was so infinitely much more fun for the dog too if it wasn't caged in house or on a leash it's whole life.
the instant everyone had to leash their dog regardless of size or breed and walk their dog every time it had to go, people almost immediately started going with larger dogs and more aggressive breeds since the obvious and huge ownership advantage of a smaller dog and non aggressive breed was totally eliminated by the idiocracy, and the number of serious dog/man encounters went up many times and were many times more serious, than when dogs were allowed to run.
want to stop serious dog/man encounters, just go back to giving dog owners a gigantic incentive not to have big dogs and aggressive breeds.
i lived in both the universal leash law universe, and in the universe where smaller dogs of non aggressive breeds could run their yard and street freely, and the run freely universe had literally a very very small fraction of serious incidents, just because everyone was incentivized to have smaller dogs and stay away from breeds like pits..
and besides the far far fewer serious incidents then, it was also 100 times better for both dog owners and dogs.
leash laws outside large metro downtowns have been a complete and total disaster, and had the exact opposite effect as intended to boot.