No. It's a false argument meant to distract from their discomfort with homosexuality.

There have always been gay people. Every civilization in history has had them. You won't find a single credible historian that will link acceptance of a gays to a collapse of any society.

Correlation is not cause. The collapse of any civilization has numerous causes. Things like climate change (localized and global) in the form of drought and crop failures, disease, and politics(war, trade, shifting borders), and natural disasters are responsible for civilization collapses.

As an aside I don't even like the idea 'civilization collapse.' Sure empires rise and fall, political philosophies fall out of favor, and governments fail, but the people of those civilizations still inhabit the same lands. Comments like the ones you heard on the radio really only illustrate the ignorance of the people making them.

Rather than take this question at face value and assess this claim based on the history of marriage traditions (for which Stephanie Coontz's "Marriage, a History" would be worth a read), what constitutes a "downfall of civilization," etc., I would address this question from a completely different perspective--rhetoric.*

Rick and Bubba (disclaimer: never heard of them, never listened to them, but I'm familiar with these arguments) are claiming that same-sex marriage (and general acceptance of homosexuality by extension) = societal downfall.

I would argue that R&B are not particularly interested in listening to historical evidence either in support of or contradictory to this position. What's at stake for them (and their listeners) is not the truth of this argument, but what this decision means for them and their worldview (weltanschaaung if you wanna get really fancy--I am writing this naked save for my rainbow top hat and glitter cummerbund, after all).

Up to this point, people with opinions like R&B (in the US) could generally assume that they held the moral and social high ground. They could generally assume that most people sided with the implicit or explicit belief that homosexuality was sinful, deviant, and not equal to the rights assumed by heterosexual folks.

But as of today, by the grace of a 5-4 vote, they and their ilk can no longer assume that the prevalence of this opinion is the majority. From now on, this belief will always have to assume the defensive, rather than default position in an argument.

And that reality now presents a major threat to what they perceive as the reality to their world. For R&B, this claim is absolutely true...to them. The acceptance of marriage equality is and always will be the scapegoat for which they will blame other ills.

What's at stake is not historical evidence--they could give two shits as to whether anything like this ever existed before (and it has). What's at stake is the SYMBOLIC destruction of a worldview that has been crumbling at a precipitous pace for the past ten or so years.

...not that that answers your question, per se---but I think this approach is much more fruitful than getting in a "facts fight."

(Thanks for the mention, /u/chicagofirefifa3.)

*I've noted before that I got my Ph.D. writing on the history of sexuality, prostitution, etc. Hence the flair. But my discipline was Communication Studies, specifically Rhetoric, which focuses on the history and philosophy of argumentation, persuasion, and social influence. This is why arguments like the gem from ol' R&B are much more interesting from a rhetorical perspective, rather than a factual perspective.

This is an interesting trope among conservatives going back at least to the nineteenth century. You see it in anti obscenity campaigns in the US, UK and Ireland. I saw a suggestion that the discovery of large quantities of sexualised art in Pompeii may have helped to create the idea of Roman decadence but I don't think it has been systematically investigated.

Follow-up question: what "civilisations" are actually provided as evidence for this argument? I've heard the argument applied to Rome, but don't remember anyone else.

Juvenal wrote about homosexual marriage in his Satires. Made a big deal at the vanity displayed by leaders of warriors putting on make up before the fight. Also, pointed out the fact that gay people can't bare children.

I think it's in the second Satire.