There’s a major values disconnect here. The ones promoting comprehensive sex education range from “it’s totally fine, as long as it’s safe, consensual, and among similar ages” to “we really shouldn’t encourage it, but while far from ideal it’s not the end of the world, we might as well equip them to be safe”. The “if they’re going to anyway” language is largely a conciliation towards people near the latter end of that scale.
The ones promoting abstinence-only education mostly go well beyond “far from ideal”. To them, it’s just plain morally wrong. STIs and unwanted pregnancies are just punishments for moral failure. (Though this gets weird when pregnancy becomes both a blessing and a punishment. That’s not actually a contradiction, as the opposite of punishment is reward, it’s just weird.) Teaching kids to be safe is like teaching potential criminals to not get caught.
This metaphor doesn’t land because it presumes that nearly everyone sees adolescent sex as a severe negative, similar to how most people would see steroid abuse, it’s just that the sex-ed promoters are recklessly tolerant of moral failure for some strange reason. The fact that the people they’re aiming this metaphor at simply don’t see it that way renders it incoherent if one doesn’t know where they’re coming from… and fails to provide any reason to change their views if they do.
(Side note: Steroid *use*, not abuse, is perfectly legal in most countries. One can use them in moderation, and while under medical supervision. Though if you plan to go pro, you need to be off them for long enough for it to be undetectable. So while the general public might have an ignorantly unjustified view of steroids in general, for those in the know, it doesn’t quite work on this level either.)