Tigers are great animals and have a bad rep for eating people but are really quite loyal and friendly. (I actually know a guy who owns one no bullshit.) that being said most people rightfully steer clear for fear of being eaten.

My Doxie and Yorkie can never kill a human being not even if they want too. But a Pitt especially when it sees a smaller dog, (even the best trained) often have a bad attitude and can fight or kill them. Add a human owner who gets in the way and blammo human attack, (although it may be unintentional or in self defense).

Every Pitt I know is as you say friendly and a great companion dog, you'll get no arguement there. But since most Pitts aren't socialized with small dogs, (chicken and egg not sure if people don't like them near their pets because they are dangerous or they are dangerous and because people won't let them around their pets) but the end result is the same.