I partially agree with you. I think it's really all about where the emphasis is place in the education, though. Do you emphasize not having sex until you are ready for marriage/kids/etc. or do you emphasize safer sex practices?
All sex education classes, to my knowledge, emphasize abstinence. Mine certainly did. More importantly, they clear up misunderstandings about the bodily and emotional changes that go on in the teen years. I have never heard of a sex education class that actually emphasized sexual activity among teenagers. Usually, the classes dwell on family planning issues. You don't need a lot of class time to explain how contraception devices work, but you do to explain human anatomy, pregnancies, STDs, and the effects and costs of child-rearing.
Put another way, what if we are talking about drug education? Do we assume that the students are going to do drugs anyway and teach them about using clean needles, where to score "good s**t", how not to get busted, etc?
Clean needles and lectures on AIDS yes. Avoiding arrest and scoring "good s**t" no. It helps to give people information about the temptations that they will face, the consequences of giving in, how to deal with those temptations, and where to get help if one does become addicted. I don't think that drug education is as controversial as sex education, primarily because sex is a very sensitive topic for many parents. The real controversy is over whether there should be free clean needle programs, relaxed penalties for drug users, and the like. Unwanted pregnancies and STDs are a somewhat different problem, since they don't usually involve the complication of addictive behavior.