However, simply calling this censorship is slightly off, it's merely addressing the knee-jerk issue. The real problem at the bottom of this whole thing has nothing to do with free speech.
Instead, it has to do with if one's open-mindedness is so very open-minded as to induce genuine harm. In a scenario out of the game, we don't walk through a park and see a man raping a screaming 10-year-old girl, shrug, and keep walking, thinking to ourselves, "well, who am I to judge?" So there's a definite limit to how open-minded you can be before you're condoning harm. In other words, there's a point where being open-minded is no longer a function of intelligence, but rather an irresponsible lack thereof.
Creating games about raping people is pretty close to that line. It's a bit of a stretch to say that a game like RapeLay will definitely get a person to start raping people, even psychological experiments finding varying results. However, it's not a stretch at all to say that the open sale of such a product is condoning rape on the level of being content in a game you can buy. At the point where we're a society that chooses to condone rape on an additional level, we're that much closer to the "well, who am I to judge" scenario above.
So, when you break it all down to the fundamentals, the reason why a restriction of a game like RapeLay applies is because the harm condoning it may bring to a society is greater than the harm not condoning it may bring to the benefit free speech brings to society.