Presenting some dog bite statistics from a favourite site of mine, dogbitelaw.com:
There are 4.7 million dog bite victims annually in the USA.
1,000 Americans per day are treated in emergency rooms as a result of dog bites.
In 2010 there were 34 fatal dog attacks in the USA. Most of the victims who receive medical attention are children, half of whom are bitten in the face.
I'd imagine that the proportion of dog-kills in the US is the same as in the UK, per capita.
And the types of dogs that kill? There's a study for that too:
Pitbull-type dogs were involved in approximately a third of human fatalities caused by dogs.
Rottweilers were responsible for about half of human fatalities caused by dogs.
It's generally estimated by multiple studies that Rottweilers and pit bull-type dogs account for between 65% - 80% of fatalities, but those two breedsalone definitely didn't make up that percentage of dogs owned at the time of the study in the US, so there's definitely an issue here with those two being psychotic murder-dogs.
The reasons for this? The Economist put their view forward a few years ago: "First, the pit bull is quicker to anger than most dogs, probably due to the breed's unusually high level of the neurotransmitter L-tyrosine. Second, pit bulls are frighteningly tenacious; their attacks frequently last for 15 minutes or longer, and nothing—hoses, violent blows or kicks—can easily stop them. That's because of the third behavioral anomaly: the breed's remarkable insensitivity to pain. Most dogs beaten in a fight will submit the next time they see the victor. Not a defeated pit bull, who will tear into his onetime vanquisher. This, too, has to do with brain chemistry. The body releases endorphins as a natural painkiller. Pit bulls seem extra-sensitive to endorphins and may generate higher levels of the chemical than other dogs."
However, the good people at dogbitelaw.com are keen to stress that 'Any dog, treated harshly or trained to attack, may bite a person. Any dog can be turned into a dangerous dog. The owner or handler most often is responsible for making a dog into something dangerous.'. So there is the possibility that the only people who want to own pitbulls and rottweilers are those who are likely to train them to be evil nutcase-dogs. This is a pretty strong possibility: anecdotal evidence from yours truly indicates that the only people who own pitbulls and rottweilers are people who have a criminal record instead of a CV, and who think that the Fast and the Furious movies are great pieces of cinema.
Some people might say, even if the dog is a bit aggressive, you can't blame the dog itself, it's the trainer's own fault for not training it to be civil. But if a dog requires some hugely intensive training program just to prevent it from biting kids all the time, then that dog definitely shouldn't be allowed to be kept as a pet. People can't be trusted to keep these things as pets because people are lazy and will leave the dog untrained running riot.
And of course, even if the dogs are raised perfectly, to the highest standards - say, raised by a member of the Royal Family - they still bite kids. Princess Anne became the first member of the Royal Family to have a criminal record after her stupid bull terrier bit two kids in a park. Amusingly, she was even fined £500 for it, which I imagine was just deducted out of the £40 million we pay her mum every year.
In the UK, it's legal to own a pitbull, but it's illegal to breed them. Currently, about a 1000 pitbulls roam the UK legally. For more on the failings of the Dangerous Dogs Act 1991, see LexisLibrary (it's like dogbitelaw.com but way better).
Sacks JJ, Sinclair L, Gilchrist J, Golab GC, Lockwood R. Breeds of dogs involved in fatal human attacks in the United States between 1979 and 1998. JAVMA 2000;217:836-840.