They are all fine until they aren't. Lets ignore for a moment that these dogs were bred for dog fighting and aggression was a wanted characteristic, and focus on the physicality.
If an average dog, spaniel/lab/collie etc was aggressive towards a passer by. There is a high chance that anyone over say the age of 12 would be able to hold it back. Even if it was loose, the chances of it doing major damage/killing someone are pretty slim.
The XL bullies and similar types are big, muscular and strong. Difficult for even grown adults to control and if it attacked, with that style of jaw and the tendency to grip, they can do a lot of damage in a short space of time.
I grew up with dogs, I don't hate them but I'd never have one of these types and it would be a cold day in hell before I'd allow one anywhere near children regardless if how much the owner claimed what a big softy it was.
A friend recently had her collie turn on her as its just developed epilepsy and reacted after the seizure. This is a loving dog brought up in a quiet nurturing home with experienced owners. As it was not an XL bully she was able to push it off and leave the room with just a bit of bruising for her trouble. Wouldn't be the case with one of these breed types.
Who'd take the chance?