I love Rotts, they're phenomenal dogs if trained correctly. My rottie, Ursa, is an amazing dog. She gets along well with the cats, and has no aggression towards people or other dogs (she's in training to be a therapy dog) and most importantly, is well-behaved around my baby. Of course, she's a purebred from some impressive bloodlines, and her sire and dam are excellent dogs as well. I can't attest for the ones bred irresponsibly.
You want to talk violent and unpredictable--let's talk about my neighbor's two nasty-as-hell terriers, aptly named Ava and Sza Sza.
These two little rats attacked me and my 5-month-old daughter in our garage. I've found terriers and yap-dogs to be much more aggressive and nasty than the bigger 'macho' breeds. Granted, a rott or a pit could do more damage with one bite. It's all in the training and the breeding.