I am a dog expert, and I earned that title the hard way. As a power company employee I've literally dealt with thousands of dogs in someone else's yard, and furthermore have recieved professional training in dealing with dogs.
Pit bulls are not, to my experience, inherently vicious unless someone made them that way. That is not to say they are "safe", as NO DOG IS SAFE. Any dog, I don't give a rat's ### what breed, may bite under the right circumstances. The only dog that is 100% sure to never bite is one that has no teeth.
The problem with Pitts is twofold:
1. Many people DO deliberately make them vicious, with the intent of using them as guard dogs. Drug dealers are particularly prone to this, and many dealer houses will be literally surrounded with Pitts on chains so that you cannot approach without encountering at least one.
2. IF A PITT does "go bad" or attack someone they shouldn't have, the Pit-bull's incredible musculature and powerful jaws make him a deadly threat.
I have "known" probably a hundred or more Pitbulls. Many of them were sweet and friendly dogs. Some were vicious. I have been attacked by a Pitt, once. The attack was very serious, the dog tried to kill me with great persistence. I was forced to kill the dog to prevent him from killing me.
Despite this I don't automatically fear Pitbulls, instead I observe their behavior before getting out of the truck and determine whether they are a threat... most Pits are NOT if not provoked, unless they've been raised to be vicious as I said. If I judge them a threat, I don't fool with them. If a pitbull was in my yard and showed any sign of aggression I would shoot him immediately. A "Bad" pit is no joke.
Some people want to ban the breed. I wouldn't go that far, but possibly classifying them as a "dangerous breed" and holding owners in higher liability if they get loose and harm someone might be reasonable.