Pitbulls CAN be nice dogs IF cared for properly. Labs are nice dogs, almost exclusively, except in cases of extreme abuse.
Misbehavior by the owner IS often the proximate cause of dog problems.
Back in college in the '70s, a guy in the dorm where I used to live had a big black lab named "Grover". Grover appeared by nature to be a fairly amiable dog... or would have been if his owner hadn't been in the habit of feeding him LSD.
When Grover was tripping, he could walk up to you and lick your hand, walk around the corner, come back and try to KILL you, all in the space of ten seconds.
Strangely, this was the cause of considerable turmoil in the immediate vicinity. He chased several people, myself included. He chased a friend of mine who'd been mauled by a dog as a child. Larry then returned to his room, in the process collecting a .36 Navy replica, a .58 Zouave replica and a sabre. He then went [without success] Grover hunting. In the meantime, others called Animal Control. They sent a small woman out with what amounted to a length of clothesline to tie around Grover's collar. Per SOP, Grover walked up, sniffed her hand, went away for a few moments and returned to kill her. Having more sense than bravery, she punted, leaving Grover en situ.
We complained to the school, who talked to the owner. He swore that Grover was just the sweetest natured dog. The Dean of Student Life told him to get the dog off campus, which he professed to do. He could not explain the presence of a dog dish in the hallway. Maybe he was dating Rosie O'Donnell.
In any case, the owner was told in no uncertain terms that if Grover bit anybody, Grover would would get shot, and that his prospects weren't too good either. Grover disappeared permanently.
As I said, Grover probably would have been a good dog were it not for the abuse inflicted upon him by his master.
Of course that was also the year when giving PEOPLE acid without telling them was in vogue. I kind of put a crimp in that when I casually mentioned that if somebody gave ME acid without my permission (which they'd never get) that my first order of business would be to procure my Ithaca riotgun, shoot the parties responsible and then claim I was on drugs, regardless of my actual state of mind. That seemed to take the fun out of that activity. The same people gave my best friend's cat acid. He discovered this when he noticed it attempting to jump into a tree and missing by about two feet. I talked him out of getting his Remington 1100. I told him to instead give them a "talking to" during which I would be discretely out of sight with my Ithaca in case they wouldn't listen to reason and got aggressive. They said they didn't have ANYTHING to do with it... and would never do it again...
In all too many occasions, the real "animals" walk on two legs...