Anyone who has spent any significant amount of time in conservative Christian circles has, in all likelihood, been exposed to the claim that acceptance of homosexuality heralds the downfall of a civilization. At its core, this assertion is founded on the belief that God destroyed Sodom because of homosexuality, a notion I've addressed before.
Having reached their conclusion, proponents then project that premise onto other historical situations, tailoring the facts as needed to make it fit. But do their assertions hold up? Given that anti-gay activists can't point to more than a handful of the many noteworthy civilizations that have existed throughout recorded history, their claims are already on shaky ground.
My own credentials as a historical commentator don't extend beyond a few college-level history classes and the several dozen history-related books that I've read over the years, so my own investigations into this topic don't necessarily represent the last word on anything, but in my experience even most conservative historians don't take the notion that failure to persecute homosexuals signals the imminent collapse of a society very seriously.
And what of the civilizations that activists use to support their case?
Ancient Greece is one of the first societies that come to mind, and it is true that Greek society was more tolerant of homosexuality than many. But why did the Greek city-states ultimately succumb to invaders?
Sparta was a totalitarian regime that encouraged homosexual relationships among its soldiers as a way of boosting combat effectiveness. But pushing men into same-sex relationships regardless of their orientation is a far cry from tolerating same-sex relationships among those who are naturally inclined toward them, and so it's little wonder that Sparta's population was in decline for decades leading up to its fall.
In contrast to Sparta, Athens was the freest society the world had known at that time in history, and the source of much of the philosophy and literature that we associate with ancient Greece. But to suggest that Athens fell due to its relatively tolerant attitude toward certain homosexual behaviors is to grossly oversimplify the situation that the city-state and its allies (and rivals) found themselves in.
More to the point, it's a stretch to imagine that a civilization that was crumbling due to moral laxity, as some Christians might claim, could have successfully repelled the most powerful empire in the world (Persia), against almost astronomical odds. Our history books still teach us of the incredible acts of heroism that made the Greek victory possible. That Macedonia was able to sweep in afterward and overrun the exhausted city-states (and ultimately Persia, too) can hardly be attributed to decadence on the part of the Greeks.
Judah is another potential candidate for the list, due to the several mentions that the qadesh (or male "holy ones") receive in the Old Testament. But the King James Version's substitution of "sodomites" for qadesh is a gross mistranslation; the qadesh were pagan priests who performed sexual acts with male patrons as part of their fertility rites. They were, first and foremost, idol worshipers - and idolatry was the primary reason that God sent his people into exile. Outside of these passing references to the qadesh, none of the Old Testament authors ever mention any homosexual activity that may or may not have been going on in Israel or Judah.
Rome is perhaps the empire most commonly cited in this context, but again it's a poor example. In fact, it's highly questionable whether acceptance of homosexuality could be considered widespread at the time of Rome's fall, given that Rome officially became a "Christian" nation late in the fourth century (nearly 150 years before its fall), and that laws were passed after that time that outlawed homosexual activity. A stronger case can be built for the notion that Christianity was responsible for Rome's fall, though that, too, would be untrue.
If any one factor can be cited as causing the fall of the Roman empire, it was the decision to allow several large barbarian tribes (seeking refuge from the Huns) to settle in Roman territory. These tribes never assimilated into Roman society, which eventually led to open conflict between Rome's citizens and the foreigners who now lived among them, at a time when the empire was already struggling economically.
And it must not be forgotten that the eastern (Byzantine) empire survived for another nine centuries after the fall of Rome. East and west had not had that much time to grow apart culturally by 530 AD, yet their respective ends lay nearly a millennium apart.
Weimar Germany is an interesting example of a nation that was highly tolerant of homosexuality in its final years, but even here there are extenuating circumstances to challenge whether this correlation points toward any actual relationship between the two.
Germany and its allies had recently fought Britain and France and their allies to a stalemate in one of the most devastating wars the world had ever seen. After agreeing to a cease-fire and withdrawing its troops from the front lines, Germany was betrayed by Britain and France, who broke the terms of the cease-fire in order to blackmail the Germans into a surrender. The heavy reparations Germany was forced to agree to left the German economy in a shambles, which in turn created widespread civil unrest.
It was in that atmosphere that the Nazi party was able to rise within a relatively short period of time from fringe group to major political party. If acceptance of homosexuality played any noteworthy role in the rapid decline of the (short-lived) German republic following World War One, it was in Hitler's use of politically unpopular minorities (Jews, Gypsies, homosexuals, communists and so on) as scapegoats on which the majority could focus their ire, which in turn kept the general populace distracted while those in power pursued an agenda that would lead to one of history's greatest bloodbaths.
I've also heard that Venice is sometimes cited alongside these other civilizations. Being somewhat less familiar with the history of that city-state, I can't comment on the Venetians' reported acceptance of homosexuality or how it might correlate with their decline. But given how weak the other (more popular) examples are, I wouldn't say it leaves much to bolster the anti-gay position in any case.
Advocates of this position could still argue that an accepting attitude toward at least a few forms of homosexual behavior existed at some point in the history of each of these civilizations (and, no doubt, in some others that are no longer around), but the evidence does little to suggest that this apparent correlation is a cause (or even symptom) of societal decline. By implication, intolerance of homosexuality should be a sign of a robust civilization, yet regimes that were hostile toward homosexuals litter the graveyard of history alongside those thought to be too 'tolerant.'
Human history is a subject as complex as the billions of individuals that have been a part of it. Empires rise and fall for a multiplicity of reasons, and while patterns can sometimes be discerned between them, responsible historians are careful not to overstate the significance of every correlation they observe.
If one thing can be consistently gleaned from the lessons of history, it's that the pursuit of power represents the greatest and most pervasive threat to human freedom, no matter how noble the intentions of the power seekers. Those who would use their power to impose "God's will" on others are no exception to this, nor are those who would bolster their power base by framing a minority group as scapegoats for all of society's ills.