The best pen for math notes is the cheapest ballpoint you can find at your grocerie store.

Gel smears too much and you’re going to be loaning pens to classmates so just keep a stack of cheap pens.

Huh. I can’t come up with a reason for why molesting baby Hitler feels so much more wrong than killing baby Hitler. You could even make the argument that it’s less wrong.

Is it just because of how killing and death is so normalized in all of modern media?

There is no right answer. It just depends on convention. It’s like color vs colour, neither has been shouted down from the heavens to be the only way to write something, it depends on culture.