Violent Dog or Violent owner?

I think that the majority of vicious dogs are trained by their owners to be so or have been beaten and abused so are just not trusting of people. I have had many friends with large dogs,, pitbull, rotweilers, chows, ect that are perfectly loving family members. My daughter has a little 25lb rat terrier that is the terror of the neighborhood. He is loving to his family members, but anyone else he barks his head off at and would just as soon snap and nip at them as anything else.