This reminds me of the episode of The Newsroom last night, where Maggie asks "What's wrong with being a slut?".
If they're not having sex in the bedroom they're probably having it somewhere else or at the other persons house. There isn't anything wrong with sleepovers. Nowadays I sleep at my girlfriends on a regular basis and it helps build a relationship, if anything (granted this is a good one). I think being more open about sex and not framing it in such a negative light would be best for everybody. There's nothing wrong with it if done responsibly, and saying not to do it at all as a teenager is not treating it as the subject should be treated.
I'm 21 and my parents still forbid me from being alone for too long in my room with a girl, not to mention having one stay over for the night. If you couldn't tell, my parents are a tad on the sheltering side. And they wonder why I don't bring many girls home. I'd like to think I'd be more lenient when I have kids of my own.
Herodotus wrote how the tomb of Alyattes, once an ancient world attraction, was built mainly by the prostitutes of Lydia. The fascinating part of this is those prostitutes were the daughters of the common people, saving up for a dowry. They also got to choose who they got married to.