I also believe that any dog, like any person, can be dangerous. My border collie/ shepherd looks cute and friendly but he has a terrible demeanor with strangers and has bitten before. He now wears a muzzle or is segregated when he can't be in complete control. I think a lot of owners either don't have the patience or maybe the desire to pay attention to their animal and either correct bad behavior or learn why it occurs.
I see a ton of dogs who have almost no recall and completely ignore commands, yet they are usually off leash in public forests or even parks.