I have three friends who have gone the rescue route. One had to put the dog down after he bit four people including her, one severely. One is on puppy prozac and cowers in a corner most of the time. When she is not on the Prozac she wimpers and snarls if someone comes into the room. By choice she spends most of her time in a very expensive crate my friends had custom made for her. And the last one has been banned from our yard because he has three times viciously attacked my dog for no reason. The first two are/were purebreds a cocker and a lab. The third is a beagle/boxer mix that should be put down. All these people felt they were doing the right thing.
And we’ve had 3 rescues that have been wonderful dogs, good with children, workmen, and our cats. Thy have never bitten anyone.
What’s your point?
Too bad about the bad experiences your friends had, it’s hard the know what the real problem is, but overall, most experiences are positive.