A certainly flawed analogy occurred to me about the abstinence debate. Adolescent and young adult sexuality is like the Israeli peace process.
In Israel, no one is truly against the peace process. If the hawks believed there existed some action that they could take that would bring enduring and true peace to Israel, they would agree to it in an instant. The disagreement between the right and the left in Israeli politics is not for or against peace: it's for or against the likelihood that any given action by the state of Israel could result in peace. The hawks say that the prospects for peace lie in the hands of others, and Israel has done what it can and possibly more, i.e., many actions that were useless or dangerous.
As in Israeli politics, I don't think the disagreement over sex education is about the desirability of adolescents and young adults abstaining from sex until they have lower risk of STDs and are in a loving lasting relationships. The disagreement is about the likelihood of any action by adults inducing this ideal state. The abstinence camp is idealistic like the peace groups in Israel. The comprehensive sex ed camp say that adults have very limited actions they can take, and the best they can do is containment, and that attempts to induce this ideal state are useless or possibly dangerous.
It's not impossible for either ideal state to emerge. If nothing else, when the Messiah comes there will be lasting peace in Israel and around the world and everyone will make wise sexual decisions all the time. Until then, it's not clear.
(Of course, the optimists on abstinence are usually hawkish on Israeli politics, and vice-versa. Who said people had to be consistent.)