I think some people blinded by love for their dogs are missing some very key points here.
My sister has a AB, biggest pushover you can imagine. But that doesn't mean a damn thing if one day she decides to take a bite out of someone.. The problem is the amount of damage these dogs can do in a very short period of time. That's the one common factor with all these dogs, regardless of how well you've think you've trained it.. Not to mention the pain threshold these dogs have, you could take a baseball bat to its head and it wouldn't phase it. So combine those certain attributes into 120lbs of muscle and you've got the potential for disaster.
Anyone who thinks they can predict what an animal will do is fooling themselves. These dogs (AB's for example) were bread as working dogs (to catch and hold livestock none the less).
Do I think my sisters AB would ever harm a fly? Honestly, I don't think she ever will. Is there potential for extreme damage or even death if she does compared to other breeds? Absolutely.