You got it almost right, but only almost I suspect you stopped reading somewhere in the beginning of my reply. The reason empires wither from within are usually not because of someone with a shanab dresses in a tannoura thus making it a trend among few m'shannabeen. These guys have only limited impact on the overall survival outlook for a society of our dimension. And neither do these empires collapse because in certain circles they start exercising more sex orgies than a generation before. It is rather because of much deep throat and harmful deficiencies and which people come to tolerate and learn to live-and-let-live with because they balance so subtly on the edge of normality and within the frames of what is legal.
The decay starts with the destruction and loss of credibility of the social contracts, founded on certain moral values that regulate how people deal with each other. When "every man for himself" becomes a rule more than exception, when brother conspires against brother and wife against husband, when the weakest chain (as in the weakest individuals) is neglected and not taken care of. And almost always it starts from top up to bottom down. When the head of the system sways and becomes ripe to fall, the rest of the construction follows down. Few superficial manifestations of odd fetishes caused by sudden mental deviation from the norms do not cause empires to collapse.
Even if you gather the entire population of the lgbt in an independent own country and arm them to their teeth they wouldn't at any rate represent a threat to humanity's ongoing evolution, not even a fart against its progress towards wanting to expand its self-multiplying drive. When I hear people expressing their fears against these people's intentional or unintentional damage against the natural mechanisms for mankind's reproduction, I wonder how come nature itself missed this little detail and produced them after all.
the decay does not come out of the blue. the decay itself is a manifestation of other deeper illnesses that eat away at the foundation of society. brother does not turn against brother and wife does not turn against her husband out of the blue. they do this when morality and ethics dive below the minimum threshold required for man to rise above and tame his imminent desires and primal instincts.
intellectual and cultural decays are a precursor to ethical and moral decline, and that usually occurs when the wealth and power of a nation outgrows its ability to handle and process it. it is at this stage when the population begins to find that its basic physiological needs are met that the masses begin manifesting themselves at higher levels that they are oftentimes not quite ready for. and it is at this stage that morality and ethics suffer a blow if the cultural and ideological pillars are not on par with the economic welfare of the society.
in this day and age, the perversion is not with sexual deviance that has existed throughout all of human history, the perversion is rather in the many groups working to normalize all kinds of perversions, in particular intellectual, cultural and ideological ones. it is at this stage that brother turns on brother, wife turns on husband, and the moral compass of nations stops pointing north.
this is the very reason why gay rights should be approached through no other venue except that of human dignity.