Not sure what all the penis stuff is but outside of that, I kind of get your argument. There is an important difference though.
A gun doesn't kill people. A bicycle doesn't kill people. In the case of guns, people are killed by other people (or by themselves) using guns either intentionally or by accident, but a gun doesn't just walk over and shoot someone. A bicycle doesn't just roll on over and kill you. Whereas a pitbull absolutely does just walk over and eat a child's face.
I don't know that pitbulls are any more predisposed to biting than any other breed. Some pitbull owners are right when they say their dog is the most gentle sweet dog ever. They can be incredibly sweet dogs. The problem is their bite is just so much more powerful.