Yes, there are video game taboos, but more often, its a matter of social taboos. More importantly, can anyone here think of a game that could be genuinely improved by breaking one of these sorts of taboos? Take for example the "Killing children" thing everyone goes off on. The only thing I can see is an extremely mild bit of added realism to the whole, "Dicking around and randomly killing things" experience.
More often than not, there are games that have broken said taboos, but done it so well that it is perfectly understandable for the game to contain it. Such as Silent Hill. All sorts of terrible things are done to children in that series, from abuse and neglect to downright setting 'em on fire. Few people call the series out on it because it takes notes from the, "tragedies that really do happen in life, and how most people react to them," book. Unless you're completely apathetic or just plain sick, you comprehend these events as a representation of the horrors of life.