I find it very interesting when people talk about "well then I found out that s/he had had a terrible childhood and had been abused themselves" because, to me, isn't that absolving them of personal responsibility?
I'm one of the many who had an absolutely awful childhood. My dad took great pleasure in battering my brother and I for any reason or no reason at all. We were punched, slapped, kicked, thrown against the wall. Verbally abused and terrorised. Starved. Deprived of liquid in the summer - we weren't allowed to even get a drink of water from the tap if he was in that mood. I remember regularly biting my tongue, hard, to produce saliva because my mouth was so dry.
As an adult, I was NC with him for years, and moved house several times and he didn't know where. He eventually tracked me down via my business, and sent a letter to my workplace asking to meet up.
I had strong reservations, but DH and I went. He said that he was sorry if he "maybe wasn't the best dad" but that he'd had a "tough upbringing from his dad too". I said "so you're seriously telling me that you think that that was the right way to bring up a child then?". He didn't answer.
DH and I walked out and I never saw him again.
I had decided while I was still a child myself that I would never have children of my own, but I can assure you that despite or because of him, I am a gentle, kind, patient and loving person.
If I committed a terrible crime though, I would like to think that I'd take full responsibility for it, and not blame it on my bastard of a father or my damaged upbringing.