I have just read books by two of his partner's May Pang and Cynthia Lennon and i have to say there is plenty of stuff that isn't great about John.
But I think it's wrong to see him as simply a perpetrator, as far as wife beating he hit Cynthia once according to her and he was contrite and didn't do it again. But John didn't have a good upbringing what strikes me is that he was probably the most fragile Beatle, he lost both parents, his mother might have been fun but she did stuff that wasn't appropriate and then Mimi was also a piece of work she was abusive, selfish and Cynthia witnessed at least one occasion of physical violence, I suspect it was not the only one. John's uncle who was the more caring surrogate parent died too, then his best friend Stuart. Johh was damaged he had demons that i think he never conquered but he made great music.