That's only because they have the power behind the punch. If chihuahas were 150 lbs, they'd be killers also! There are bad dogs in every breed, some made that way, some are just bad dogs. Unfortunately, dogs with power to kill are the ones that get the bad rap.
Yea, and its just mere coincidence they are the chosen breeds of junk yard owners and crack dealers everywhere...... Be serious.
A 150# chihuahua would be as dangerous as the velociraptors in Jurassic Park!