Because taking things to an illogical extreme conclusion always makes them clearer.
Surely the bizarre extreme opposite of that is that we allow everything in games, they should be programmed to allow you to commit as many disgusting acts as you like. Where would be your personal line in the sand on what you think should be added to allow you to roleplay the character you like? How about rape, or paedophilia? Or is there perhaps a middle ground, where theft and murder against adults are seen as part-and-parcel of games when our stories and media have been fascinated with them for decades, and in a violent, unfair fantasy world (made by people living in this one) they can even occassionally be justified, but there are still some things that are just tasteless for the sake of being tasteless?
Sure, people make and watch torture-porn films like Hostel, but that title is made with shock in mind, and isn't for a mass audience.
Treading that grey line between realism, comfort, empathy, shock and disgust makes for an interesting discussion, reductionism doesn't.