You are decontextualising violence there. I can play a violent video game where I kill Nazis without much problem but I won't play a video game where I am a Nazi soldier fighting for Nazi Germany.

Even in Issac there is some justification to the whole scenario since the mother is abusive and not to mention the supernatural nature of the universe the game is set in. Would you play a video game where you psychotically beat up your warm, kind, lovely, caring mother for no moral reason? This is not just about trying it out once out of morbid curiosity. But trying it out over and over again and then complaining on an internet forum that the passerbys in the game are not letting you beat your lovely mother senseless.