I’ve never played Mortal Kombat; the closest I’ve come is Diablo and Diablo II.
I think that, as long as you can keep the violence and immorality in the world of fantasy, not bringing it to the outside world, you are OK.
This isn’t as easy as it sounds! For example, if I’m running a sorcerer character, it’s easy enough to know that he/she is fictional; and that sorcery is a sin in the real world.
But there are helper characters that, once you’ve heard their spiel, you don’t want to listen to it again, so you just hit the “leave” button when you’ve got what you need from them. That kind of rudeness is a good deal more subtle than the fictionality of a character.
I remind myself frequently that this, too, is not acceptable in the real world.
So you have to know yourself to know whether the games are good or bad (or between) for you.
Take Kristina’s excellent quiz!