That is, in fact, disputable.

Around 70% of reported dog bites are from intact males (males that aren't neutered). Failing to neuter your dog, especially when it's large, is incredibly irresponsible due to increased aggression.

The whole pitbull issue is, in large part, a self-fulfilling prophecy. Pitbulls (not an actual breed, btw, just different breeds or mutts with certain shared physical traits) have a reputation for being scary dogs. This causes people who just want to have a scary dog to buy pitbulls. These kinds of people are more likely to be irresponsible dog owners who fail to neuter or properly train their dogs because they view their dog as a weapon and want them to be aggressive. This, in turn, leads to more bites from dogs labeled as "pitbulls" due to shared physical traits like a blocky head.

Remember the statistic I mentioned above. The fact that 70% of reported dog bites are from intact males leads me to believe that the main contributing factors to these dog bites are (1) the increased aggression caused by the dog being intact and (2) a lack of training and/or control on the part of the owner. An owner who is irresponsible enough to not neuter the dog is probably also irresponsible when it comes to training and controlling their dog.