On one hand, can there ever be such a thing? After all, games - just like films and books - are an art form that has to tackle difficult subjects in order to express themselves.
But on the other, sometimes things can go a little too crazy, becoming taboo and inappropriate simply for the sake of it, as though a game is entirely determined to get a disgusted response from the viewer for the sake of the controversy.
While it is nobody's place to fully judge whether a game has "gone too far" and become too offensive or disgraceful to even exist, it is important to remember that just because art has a message, it doesn't mean that it's right, acceptable, or even any good.
So with that in mind these games have all for one reason or another, proven themselves to be filled with the type of taboo subjects and challenging themes that simply aren't fit for mass media.