Over the years humans have bred animals for different characteristics: faster horses, leaner pigs, different looks in pets…and aggression. It may be contrary to popular belief that genes play a role in behaviour, nature not just nurture. But we must not let sentiment triumph over science.
To determine if pit bulls (bred for dog fighting, a sport more popular than ever and not just with rappers) are more dangerous than other breeds you would need to know the population by breed. This can be had from the United Kennel Club and American Kennel Club. Then one would need to know the frequency of bites by breed. No one keeps such statistics and many would be unreported. But deaths by dog attacks are kept and kept by breed. As Stanley Coren points out in a 20 year study (1979 to 1998) by the U.S. National Centre for Injury Prevention and Control, of the 238 dog-bite-related deaths, pit bulls accounted for 98. That makes them 80 to 100 times over what their population percentages would expect.