The only thing that I ever see on mainstream film and television is passionately kissing couples and people under sheets recovering from post coital activities. If I recall correctly, that's not what sex is. I think we need to step away from our prudery so that sex can be exhibited in an artistic manner.
i don't mind teenage roles that are sexualized, because let's face it, teens have sex. To portray a teenager as a pure virgin is unrealistic and unfair. If anything, it's just a reenforcement that girls (because let's face it, that's who is usually targeted) need to maintain a squeaky clean image even if she is having sex. Which isn't right and just feeds towards double standards.
And for those with kids, if you don't want your kids to see it, turn it off. It's very simple. I don't like having tamed television just so we can protect kids (job for parents, am i right?)