To be fair, I don't think showing a villain having a crappy childhood is meant to "excuse" anything they do. It may humanize them, but it doesn't absolve them. If anything, it makes those heroes that have had crappy childhoods all the more heroic...they faced those same kinds of things (or worse) and overcame them, whereas the villains were too weak in some form or another and let it consume them.

Still, it's pretty clear Norman's shifted a good bit away from where he was originally conceived, from someone that was a ruthless businessman but not altogether evil to...well, someone that was (and bats**t crazy to boot).