Comment by mos_basik

The more complete version of this line of reasoning is (which I've seen more than once, but no links to hand, sorry) is:

After solidly internalizing the messaging of "teen pregnancy is the worst thing ever" & "sex leads to teen pregnancy", there's no "switch" to make those thought patterns disappear without a trace at the point at which it's "ok" (by whatever metric is relevant to the individual) to participate in sex, child-rearing, etc. So individuals find themselves dealing with long-term guilt at having sex and/or aversion to having children, neither of which is "rational" according to their values but which nonetheless is real and affects their behavior.