There’s another problem with “abstinence-only” teaching: what happens after marriage? So lets say you manage to scare or convince teens to hold off sex until they are 18 and can rush to get married. And then?
Either you gave them a full, factual information on how sex happens: not just “insert penis into vagina and make babies, anything else we don’t talk about” but “if you masturbate, you can find out where your personal erogenous zones are, because they differ from person to person” and “it doesn’t have to hurt the girl the first time, if the guy uses the right technique and patience” and so on; plus “now that you are married, but both want to go to college, or only the woman can find a job, so you don’t want kids right away: here’s how you use a condom, the pros and cons; here’s how you use a pill, the pros and cons etc.”
Because otherwise, who will give facts, not scaremongering, to the 18 year olds once they are legally married, but don’t want to boink out babies every year for health reason, or just want to enjoy sex (if it is a gift from God in a marriage context) instead of it being fun for the guy, boring for the woman?
Is the pastor going to tell them during the pre-marriage course (though that is not obligatory in all churches)? Where does he get the qualification to teach about biology and medicine?
If not the pastor, where else? Does the couple know they need help and facts, or have they been told “Sex inside a marriage is wonderful” and don’t understand why it doesn’t work for them without any information or experience?
In some societies, a teenager reaching puberty had sex with an experienced adult to learn how to have successful, satisfying sex and because an older partner was more patient. Obviously that model has problem points, too, but both partners being inexperienced in practice and lacking theoretical information is not a good recipe for all other areas.
When we teach driving, we have found that having an experienced driver on the passenger seat for the first year (learners permit) reduces greatly the accident rate, because letting a young person (and being above 18 makes legal but not yet wise) with very little experience do something that can be dangerous can end badly.
But with sex, some people believe that ignorance makes it better. On what rational basis?