The one thing I do not get about the rating system is, that rated R movies are for 17 and older in the U.S. Some movies and shows have some hardcore **** in it. Rated M games are for 17 and older in the U.S, but if a ****** is shown, the media shits bricks. I could understand such a reaction in rated T and E games, but a rated M games is for mature audiences ONLY; it makes the media's reaction seem illogical and stupid.
I think the only argument is that unlike movies which is a passive experience where you just sit there and watch, videogames actually requires you to be active with it. So In a movie I can see a human female and a blue alien female have mild sex on screen in a R-rated movie and nobody complains. But when that happens in a videogame (Mass Effect 1), then it is a big deal because it required to viewer to "participate" in it by choosing to go forward which such scene.
That is my opinion on what the opposing argument may be. I however think its stupid. MANY R-rated films feature sexual content in a heavier and more explicit way than M-rated games and yet videogames are the ones that sees the most complaints.
I guess it is cause no matter what, videogames will always be seen by many as a child's toy unlike R-rated movies. Also with R-rated movies, the visuals are real as it is being acted out by real life people. With videogames, it is pixels, which makes it seem "perverted" in the same way a cartoon sex scene may be.