Why is sex considered worse for children than violence?

[white_wolf]

I'm browsing the forums for a video game that is currently in development, it is an RPG and a poster made a long post asking the developers to not include any sex scenes in this game because her son wants to play it and she doesn't want him to be "corrupted." The company(Bioware) did get involved in a scandal on Fox News for a scene in their game Mass Effect, but nothing was shown it was all implied after a long story arc, of course Fox being Fox didn't even play the game to find out about it and just blew the story out of context.
Ignoring the fact that that OP is clearly a troll, her rant got me wondering about something I've seen a lot. A lot of parents will raise hell at even minor nudity or sexual scenes or implications in games,movies, tv shows etc, but are fine with their kids playing really violent games where you kill 100s of people or watching really violent tv shows, movies, and I don't understand the double standard. I'll be honest, I don't have kids, but when I do I'd much rather find out they've been having sex behind my back, safely, than find out they hurt or killed someone. Though honestly I don't think the media has that much influence on people anyway. Getting back to my question, why is sex considered so much worse than violence?