Quote Originally Posted by wolf_Q
Prey drive and human aggression are NOT the same thing. Just because a dog would attack a swan does not in any way mean the dog would attack a human.

I have siberian huskies. They would love to eat any small critter/bird/etc. they could get to, but I do not let them off leash and give them the chance. They are also often around small children and are perfectly fine with them.

The dog definitely should not have been off leash. No, all staffies are not vicious, most of the attacks you hear about involve dogs trained for fighting, or simply left intact and neglected, they need proper socialization and training. I do believe they have a higher tendency (as well as several other breeds) to be dog aggressive and they require an experienced owner.
Well said and exactly the same point I keep going back to on this thread.