Natz comments: What you say about societies not being able to reverse “sexual liberation”, this would make sense theoretically if we consider that people never really understood any deeper significance of the traditions associated with religion but instead followed it because of rational self-interest and biological/evolutionary drives. So in the past people avoided a lot of promiscuity because it was too costly for the individual and for society not to do so, whereas today the costs associated are less apparent. Today one can have thousands of children or have children with only the best males, or at least that is what ones feelings say, of course condoms and so forth will most likely be used.
It would make sense to me that the point where the incentives will change back to being in favor of more traditional modes of sexual conduct, would be a population collapse or being conquered by some other people (or both). Hopefully what could happen today is that the condom-worshipers simply die out and are replaced by the part of the native population that is more fertile and traditionally minded. This would probably coincide with a great economic upheaval, which would help promote that re-emergence of traditional sexual morality, so it seems plausible it could happen this way.