Your points are irrelevant, we arent talking about your "circle of friends" we are talking about a human aggressive dog that was put in a situation where it could attack humans. Any way if you want to get fussy about guard dogs then we can go on to say how pit bulls arent guardian breeds, they are game bred terriers, but that also is irrelevant.
No, you see good guard dogs are trained to protect, attack and release on command, not out of their own free will.
So this dog you say was trained to attack whenever an arm poked through the fence. Hah! doubt it. The child wasnt waltzing through the yard and into the front door, no, if a dog cant tell the difference between someone threatening the owner and an arm poking through a fence then he dog is poorly trained and unstable.
I doubt it was even trained, just some punks wanting a pit bull because they are so cool "Haha its so funny when he barks at people walking past! Haha look at him trying to get them through the hole in the fence! Oh pit bull, you are so funny. Lets encourage and laugh at this behavior"
A well wounded and trained guard dog will not attack anything and every thing that pops through the fence. If a dog attacks a child then put it down, there is no place for a dog like that at all