(emphasis on proper)
People are growing up and not being taught how to deal with their sexual feelings. We sweep these feelings under the rug, because they make us uncomfortable, and because we think there's something wrong with sex, but these feelings aren't just going to go away. People are left to fumble around in the dark, learning on their own what to do about their sexual feelings, and some of them are making bad decisions. Those bad decisions are used as examples by the anti-sex crowd to "prove" that sex is wrong and dangerous and immoral. So it gets swept even further under the rug, but it still doesn't go away. More people grow up without learning that there are ways to deal with their sexual feelings that don't involve victimizing, objectifying, whatever, other people. They are forced to choose between repressing their sexuality (unhealthy) and indulging their sinful desires while taking advantage of others. It is irresponsible not to teach people how to deal with their sexuality, and it is unethical to teach them harmful beliefs that involve the requirement to feel dirty and ashamed for experiencing natural desires that are not voluntary.
I had sex ed in school, but I learned very little that was useful. We studied reproductive anatomy, but learned nothing about the practical mechanics of sexual intercourse. We were shown what a pain in the neck pregnancy is, but they failed to emphasize how good an orgasm feels. We were preached to about sexual morality (i.e., sex is immoral, so don't engage in it), but not instructed in sexual ethics ("don't have sex" is not a good ethical code). A speaker came in to talk about how amazing abstinence is (and how gross sex is), yet I'd be willing to bet a teacher would lose their job if they told the class to go home and have an orgasm as homework. Sex ed should be fun, not dreadful!