To a certain extent, that's irrelevant.
Just as there are certain "inalienable rights" that all humans share, there is also a certain morality all humans share. For example, look at stories about people who escape cultures steeped in physical or sexual abuse. These individuals, while raised in such environments, know on some basic level that the atrocities they are experiencing or expected to dish out are wrong.
I don't care what culture a person is from, everyone knows that putting people in ovens or forcing them into showers that are without water is wrong. That's why so many evil people at the end of the day try to hide their crimes and cover up the evidence.
Of course, this does not mean there are mitigating factors. Mental disease or defect might skew a person's moral compass. Some people are deluded or brainwashed or conditioned to accept a certain amount of depravity as normal and acceptable. At the end of the day, however, everyone knows smashing babies against rocks is evil.
But that's reality and not a fictionalized universe created to entertain and provide intellectual thought exercises.