I agree that all dogs have the ability to turn on you. I worked at vet's office for three years and will be the first to tell you that we very rarely had to muzzle a 'big' dog, even Pit Bulls. Generally, we had to muzzle smaller dogs, particularly Pomeranians and Chihuahua’s.
However, I have to say that pit bulls scare me simply due to their ability to lock their jaws when attacking. I own two small dogs, Shih Tzu's, and big dogs in general scare me, as my dogs can easily become a treat. In fact, my puppy was attacked by a German Shepard about 4 months ago. I was able to get the Shepard off of mine and right to the vet (he's just fine now). What would terrify me about a Pit Bull is that should one choose to attack one of my dogs, my dog would be dead. There is no hoping in getting a Pit to unlock his jaw when attacking.
I think it's sad that Pit's have been breed to show aggression, even though this is not true of all Pit's. Unfortunately, for the responsible Pit owners, those that want the dog just to look cool or tough and do not properly train and control them, make a poor name for those of you that do.