I would say not necessarily violent owners as ignorant owners - and this results in all sorts of problems not just the headline causing viciousness.
I regularly see two types of ignorance that result in problem aggression - the first is failing to understand dog society and how a dog thinks it fits in to a group. The second is the idea that a dog needs to be trained to guard, which especially causes problems with some of the specifically bred "guard" breeds.
The first becomes a problem when either through natural bolshiness or a feeling of insecurity a dog feels it is either the alpha animal or driven to take on alpha roles such as protecting the pack. These are the situations where you have a "loved pet who never did anything like that before" bites a family member "for no obvious reason". The real story will be that the dog has been giving indications for months that this is going to happen because it thinks it is alpha and nobody has responded to the indications and put the dog firmly at the bottom of the pack, and as far as the dog is concerned a subordinate animal sitting on the alphas couch is a very obvious reason. Either that or a dog feels its alpha is too weak and it must take over alpha roles without becoming alpha and you then end up with a nervous animal that is likely to bark and snap at strangers visiting the home.
The second can be a real problem with the likes of Rottweilers, Dobies, GSD, Schnauzers etc when someone goes out and gets a puppy specifically to become a "guard dog" and finds that the puppy is happy and playful and loves everyone and does not so much as try to object to someone taking its toys even. They make the mistake of thinking that in order for such a dog to guard it needs to be taught - and they set about teaching the puppy to growl at someone taking its toy, encourage it to bark and run at visitors etc. Then some when between 9 and 18 months the natural breed instincts kick in - and you have an owner with an animal they cannot control that is downright dangerous.
If people spent some time doing research and learned to understand dogs a bit better before getting one there would be a lot less problems. I know there is a problem with some people teaching the animals to be violent deliberately but I have seen far more problems caused by just ignorance.
