As long as whatever influences experienced in games are not influencing actions done in real life that lead harming self or others, I'd argue that you can kill all you want in games.
I know I do and I still don't kill or harm folks in the real world!
Idk, there is some line there. Like even as a teenager playing gta, i would just plow through people and never thought much of it. On the ps2 (i think) i had a game that i have no idea what it was called, maybe something anarchy blabla. The game was just mowing down people in a mall. Like much crazier that gta, or any game that i played really. It was kinda satisfying in a weird way.
But then there is my friend back then who was always a bit... Odd maybe. He would proudly show me how he kidnapped women in gta and tortured them in game and laughed his ass off as if it was the funniest thing ever. That's all he ever did in any game that would let him. It was super uncomfortable to watch.
When I play Fallout (3, NV, 4), I am a horrific monster. I will stalk NPCs for quite a while, doing my best to stay hidden. I watch them interact with other NPCs. I follow them to a secluded place, and they are mine. It's always a melee weapon of some kind. First, I feast. If I have Dine and Dash, I'll always save it for later. Then, I will strip and dismember the remains. If I'm able to ensare multiple targets in a close proximity, I will make a pile before the dismemberment for others to find. Otherwise, I'll drag them away where nobody will ever find them. Sometimes, if it's a really good day, it can be entire settlements.