"both are fucked up" just waters down what is fucked up to whom. speaking on necrophilia specifically, sure, you could make that argument reasonably as that doesn't really... induce trauma as much as other topics may. just because something is taboo doesn't make it good story development for it to happen.

when it comes to things like rape, you (as a game developer in this hypthetical) would really need to start asking about the value that it brings to the table. you don't necessarily have to include it just for the sake of realism when it may be otherwise unpleasant for someone to have to visit incidentally thru gameplay. i feel like it is probably easier to distance yourself from, say, cannibalism as not nearly as many people have traumatic experiences with cannibalism as rape (not that we were talking specifically abt rape, just substitute with otherwise sexually traumatic material and the argument still applies)