i have a 3 acre dog park within 1/2 mile of my house. Between my wife and I we are there 5-7 days a week in nicer weather. Every single dog on dog fight I have ever witnessed first hand in th park has aways involved at least one of the more aggressive breeds (pit bull, papillon, rottweilers, cocker spaniels, etc). In the same fashion every human on human fight at dog park had at least one human owning one of the above mentioned breeds. I believe certain breeds are predisposed to violence, aggression, attacking, etc. Whenever you have to say "a properly trained pit" or a well behaved rottweiler" is a indicator to me that you are fully aware that the breed is aggressive/problematic. My therapy dog has been attacked twice in her life, both times by pit bulls, both times in dog park.
I agree that someone who spends the time, effort and money to properly train a pitbull reduces the pits chance of attacking. However take a lab, never train it and mistreat it and it still wont become aggressive. I question the owners of aggressive breeds as to their intentions.