It's hard but stop over analysing it. As others have said, a crap childhood does not give one a free pass. I do sympathise though as I have one of those, I just used to feel pity for her, but now I know she should not have been sharing those details of her childhood with me as a child and that two things can be true, she had a poor childhood and is emotionally damaged/not very bright but also she shouldn't have had a child and her parenting was poor. Having my grandad living with us (unnecessarily as in it wasn't some desperate situation when I was a child and then a few years later when very drunk telling me and my dad that he had abused her when she was a child, awful to happen but also why did you let him live with us??
I've said this on loads of threads but it's the analogy of the snake bite. If a snake bites you , you don't stay there and try to work out why it bit you, you get away as quick as you can. The snake may have had poor role models growing up or may have had a lovely childhood but the effect of the bite is the same!