I don't think there's any such thing as "teaching abstinence", no more than you can teach "liking jazz" or "wanting to travel to Europe."
I disagree. I'm not proposing we teach teens to not to want to have sex:
Teens will either want to have sex or they won't
I'm suggesting we teach them what they should desire. Just that we explain openly and honestly what their options are.
...how to express those preferences and defend them against peer pressure.
And that one viable option is abstinence from having sex, so that they have that tool available to defend against peer pressure and as a valid expression of their preferences.
The problem, of course, with abstinence is that while you're doing it you don't get to have sex.
Yes, abstinence is psychologically difficult to pull off and its a hard sale, it certainly didn't fly with me when I was taught it. Which is why I agree that we should give information to teens for how to do it safely. This, incidentally, was my school's attitude to drugs as well: Don't do it, but here are some safety tips if you do (avoid re-using needles, have a sober person around to help avoid injury etc).
Why is it necessary to accept the "moral panic" position that sexual activity by teenagers and young adults is something to be avoided at any cost?
It isn't. I'm not proposing a 'moral panic' position, and I'm not proposing that sex be avoided at all costs. Just that we teach them that having sex is risky, that the best way to avoid the risks is to avoid the activity, but if they do carry out the activity teach them how to do it as safely as possible.
Teens will decide on their own whether to have sex or abstain. We should be equipping them with the tools such that those choices are safe and respected.
Agreed. But it's better that any decision they come to is a fully informed decision (or as fully as it is possible to be). Where they are advised that it is morally and socially acceptable to abstain as an aid against peer pressure etc (overt and otherwise).