Hurro, 
m-sass,  
I note with interest the way you have attacked this particular breed, and appear to be a proponent of Breed Specific Legislation, it seems rather aggressive to me. You must be a pit bull. 
Fairly, however, in response to your idea that a dog must be genetically pre-disposed to aggression, I would argue that as it is commonly accepted that all dogs are descended from the grey wolf, and are of the genus canis familiaris, then all dogs are genetically pre-disposed to aggression. 
Of course, such an argument would rather basic in it's thought processes, so I won't do that. What I will do is cite the Herald Sun here (as the bastion of truth, and reason that it is *LOL*): 
http://www.heraldsun.com.au/news/familys-pet-jack-russell-kills-eight-day-old-baby/story-e6frf7jo-1226521785937 
Hmm, Jack Russel killed a baby and TORE THEY EYE OUT OF A TEDDY BEAR. ergo: pit bull. 
I own an AST and an SBT, and I have had a bit to do with Pits in the past.  
Here's what I can tell you from personal experience: 
1. If you're friend is missing pre-attack signals, you're not looking hard enough. With many dogs, of differing breeds, they're slight, but they're there. 
2. Signaling is dog specific, not breed specific - each dog has an individual threshold. 
3. If your highly experienced trainer was mauled by a dog under his care, I would suggest remedial training, or perhaps flipping burgers. 
But, please, tell me more about aggression and the base pairs that genetically predispose a breed...