The "viscious" dogs that I've owned (a pit bull, plus some mutts) and the "viscious" dogs that friends have owned have always been the nicest dogs to be around. Mine, plus a buds doberman both thought they were lap dogs. These animals were treated kindly & were not mis-used in any way. I really believe that the animals disposition is a standard. If it's a biter, then that's what it does. If it's not, then there's no problem. Granted, some, if not most, dogs will protect their pack (us) if they sense danger-but isn't that a good thing?
We just had to put our dog down (a mutt) because he had a history of biting & one day he decided that he didn't want to go outside when momma said it was time. He bared his fangs & had his hackles up & right then, it as decided, with all the kids going in & out of here, he had to go. We couldn't allow someone else to take him (he was a danger) so we had one VERY sad option.
the point of that sad tale is-there may be shitty decisions to be made & the owner had better have enough sense to know when it's no longer feasable to keep an animal.