That's not exactly what I meant but I can see how you interpreted it that way.
It's not that killing in all circumstances is a defective act, but even someone who kills in self defense is likely to experience remorse for having done so.
Bringing in soldier 'conditioning' as it has been described requires a whole other thread. I think it goes beyond this discussion. Mobs, wars, hired to kill like an executioner, all those are beyond the scope of a discussion of 'normal' because there are so many other variables to discuss.
So, yes, I think it is a moral norm that humans don't generally kill. There are people whose moral brain functions are defective that kill. There are intoxicated people who kill. There are people with anger/jealously issues that kill and in all those cases I would say something is wrong with them at least at the time of the murder.