It is often said that sex education can help reduce unwed teen motherhood, but rarely is the concept taken this literally. (If you're having trouble imagining what the experience might be like, go here and search for the word "pupils".) A similar argument is often made for drug legalization: that it would demystify drug use, depriving it of the glamor of the forbidden. Call it the "Tom Sawyer" argument, applied to sex or drugs instead of fence-painting. (As far as I know, it hasn't yet been suggested as a cure for rock 'n' roll.)
Proponents of this approach obviously didn't attend my junior high school, where a rigorous compulsory program of physical education never managed, so far as I could tell, to dissuade the jock students from their love of sports. In fact, the sex-instruction advocates are making an assumption that's even goofier than Tom Sawyer's: that endorsing activities that don't "go all the way" may dissuade teenagers from, well, going all the way. (I can just imagine how all those baseball-playing junior-high jocks would have reacted to a gym class suggesting that it's okay, really, to stop at second or third base.)
As I've mentioned before, it's a fair bet that an "educator" who makes lame arguments in favor of some self-evidently ineffective education method is not so much naive or misguided as indifferent, at best, to the method's supposed educational goal. And there are plenty of people who consider teen sex a perfectly salutary phenomenon, and see no reason even to attempt to discourage it. But the peer pressure on kids to become sexually active at a ridiculously early age is already enormous, and I shudder to think how much worse it will be for them in schools where the teachers are, if you'll pardon the expression, egging them on.