As long as games intersect with art and exploration of human nature then a developer should be able to explore any idea they want. If you think you have a good game idea then do it, don't let someone stop you.
I don't think I'd seek out a game with extreme content like that but there's valid game ideas to be explored with it. There are countless movies where the inclusion of that kind of extreme content made the movie better or was even essential to the movie. Games are no different. Just don't expect to be able to distribute the game without heavy pushback.
That is not the problem. The problem is idiots demanding that the game go out of its way to accommodate their fetishes. Uh-uh. The game will portray what the developer wants it to portray. If you don't like it, play another game more to your liking. If the game says "Ultima" up the front, for example, it is highly unlikely you will be able to play murder-rape-kill sim with it.
If you're going to use the artistic expression argument when making a game about extreme things then you have to be willing to accept the other consequences - poor sales, negative reviews, general backlash.
Should those "reviews" be able to talk about how much they dislike the extreme content and rate it negatively because of that? Yeah absolutely. Should they be calling for it to be banned or saying that the dev shouldn't be allowed to make it? Definitely not.
Presentation is more than half of the equation IMO. If the violence is graphic then the reaction will be far more extreme.
E.g. Should a fallout-like game have "murder-rape sim" mechanics? I think you could definitely make the argument that it makes sense in the setting. But implementing it you would have to do it in a non graphic way to make people half willing to accept it. But I think you could potentially do it. But should you? Not if you're looking for any degree of commercial success.