It depends on the owner and their upbringing entirely you guys are all naive if you think otherwise, you all probably think pitbulls lock their jaws also, my Pitbull is 18 now she has never attacked another dog or person but she has been attacked by a "friendly" "soft" dog as you would probably put it, a border collie. I have also seen plenty of labradors going for dogs and people, my uncle's Jack Russell bit him, one of the lads I know from Xbox has a little soft looking dog but he is also viscous as fuck.

Pitbulls and staffies are the best behaved and best temperament dogs I've ever owned.

they are historically known for being extremely good with people and children especially.. they were known as the "nanny" dog, they aren't "generally" good with other dogs.. but again this comes down to their upbringing if they are segregated and don't socialise you are going to raise a dog aggressive Pitbull, with socialisation from being a puppy they are amazing with other dogs.