Pit bulls used to be known in this country as "Nanny Dogs". A dog breed specifically chosen to be a companion and protector for children. A job they performed very well for over a century.
Somehow though in the past couple of decades we've gone from that to "needs to be wiped off the face of the earth". What changed? Not the dog.
Skybird has a good point about a Pits damage capability but it must be also noted that the pit doesn't have the strongest bite, or is it the largest in size and it's definitely not the most aggressive dog out there.
It's notoriety seems to be mainly media driven which is a shame.