Oh boy, another "the sky is falling" thread. These are never based on completely bonkers ideas...
First off, when I read things like "Only 6% hold to a Biblical worldview", I immediately get suspicious that whoever is claiming that has in mind only their own very narrow idea of what that means that probably only includes whatever Protestant sect they're a part of, to the exclusion of the vast numbers of other Christians around the Western world who might not be Biblical literalists or believers in Biblical inerrancy, but in all other ways (e.g., adherence to the Nicean Creed, which is this very website's statement of faith) are just as Christian as the 6% who apparently meet the OP's definition of holding a "Biblical worldview".
Secondly, there seems to be a mix-up of sorts going on here as a result of trying too hard to map the conditions of Ancient Rome onto our modern geopolitical world. To say that Rome or Greece or wherever fell due to this or that kind of political decadence and cultural ennui is one thing; to say that this was due to a lack of "national identity" is really anachronistic and weird. As any amount of forethought on this matter would remind a person, the Greco-Roman empire (Rome in the West, Byzantium in the East) was just that: an empire. As such, the formation of distinct national identities was itself more of a sign of the empire's decline than the absence of them ever could be. Again, think about it: The Ottoman Empire ruled over a very large and diverse population, just as the later Russian and British empires would likewise rule. And how did each of these end? With the rise of modern nationalism: the liberation of the Greeks, the Balkans, the Armenians, and so on in the case of the Ottoman Empire; the formation of the Russian republic in the case of the Russian Empire (soon to be transformed into the largest constituent nation of the USSR), and the formation of any number of national entities out of former British colonial possessions in the case of the British Empire (India, Iraq, Sudan, etc.). The modern concept of nationalism or the nation-state is strikingly new. When my own grandfather was born in 1911, there was arguably only one independent state in all of Africa (Ethiopia), the Austro-Hungarian Empire was still a thing, Iceland was still a dependency of Denmark, the USA still ruled the Philippines (as they would until 1946), etc. The world looked pretty different than how it does now, and that was just over a century ago. I would be willing to grant that people still had what we could think of as "national identities" a long time ago, but these were not expressed via a kind of 'supra-tribal' mentality like they would be in a modern country like the USA, where what binds people together is being 'American'. Rather, it seems obvious that the Jews of the past just like the Jews of today knew that they were Jews, as is usually also the case with regard to other groups like Armenians or Assyrians (and here I only write 'usually' because there are perhaps a great number who are Arabized/Turkified/Kurdified, and hence disconnected from their true origins), but lacking as they did during most times a suitably unoccupied homeland to call their own, these were ethnolinguistic and/or ethnoreligious designations, not modern 'nationalisms'. In other words, you were a Jew if you were raised in the religion of Judaism, had some familiarity with a distinctly Jewish language or dialect (e.g., Hebrew, Judaeo-Aramaic, Ladino/Judaeo-Spanish, Judaeo-Persian, etc.), and most importantly, if your mother was a Jew (as that is how Jewish identity is conferred as a matter of law). This is all very different than the modern western conception of "national identity". No one says "sorry, but you only get to be Australian or Polish (or whatever) if you're an English or Polish-speaking Christian".
The argument presented in the OP seems to rest upon very weak grounds. I'm not even going to touch any of the stuff about homosexuality (another strikingly modern idea, depending on how exactly it is understood) or which generation is to blame for whatever (here's a hint, though: mainline Protestant Christianity had stopped being the dominant flavor of Christianity in the USA by the mid-1980s, when even the oldest Millennials like me were still in single digits; now tell me, please: has the state of public acceptance or profession of Christianity in the USA gotten better or worse in the years since then? Hmmm...). That's all ridiculous 'culture war' nonsense that I have absolutely no time for.
