Yes, they sacked the city of Rome in 410AD, which was no longer the proper capital of the Western Empire, it was a symbol of the Empire. It had stood untouched for almost 1000 years, which is quite an accomplishment, but its sacking was a symptom of the Empire's decline and a huge symbolic blow.
There are some writers - remarkably few, actually - who lament the sack of 410. Augustine, Jerome, one other. It's actually surprisingly muted. From the few that there are, we can surmise that the event was a shock, and Augustine wrote the City of God to refute the remaining pagans around who blamed it on the new religion. But as a "symbolic blow" - by whom, against whom? As I said - the soldiers who did it were in Roman service. Their leader, Alaric, styled himself "King of the Visigoths," but the office he wanted was magister militum of the western empire. Holding Rome hostage was a ploy to try and get the government to give it to him, and it failed. Sacking the city didn't accomplish anything, and Alaric's successor rapidly negotiated a new settlement to reconcile his federates with the empire again.
These as well, but other divisions of labor that created tension among the different classes of society. The familiar outcry of proper Roman commoners about cheap labor from outside sources, essentially outsourcing of their military, and any land left to be given as a reward was either worthless or required months of travel just to reach. The rich living in lazy opulence bolstered by cheap labor while the rest scrabble for scraps from their table is something I think modern Americans can identify with.
What outcry from proper Roman commoners? I have no idea what this is supposed to refer to. The nearest thing I can think of are the conditions of the 1st century BC which led to the Republic's civil wars and ultimately the rise of the Caesars. That's 500 years before anything I was talking about, and the empire was plenty strong then and for a long time after.
There's a tendency in some of the older scholarship (like Gibbon's Decline and Fall), and in irresponsible use of it by popular modern writers, to grab a phrase or gripe from a solitary Roman writer and extrapolate it to being the universal view of millions of people, regardless of context or other sources or even the totality of what the same writer has to say - particularly when that gripe lines up conveniently with a modern political anxiety. If you want an example, I can talk about cutting off thumbs...
I do have my personal theories that the introduction of Christianity weakened the culture that made Rome what it was. My opinion is that it blunted the bloodthristy nature of a civilization that believed so wholeheartedly in its own superiority that no actions were too inhumane. If the ends were the greatness of Rome, the means were justified. Again, that's just my little personal theory.
It was Gibbons' theory too. All the smart young men became monks and focused their attention on pursuing heaven and theological quibbles rather than the practical business of law and military life. If it matched the facts, it would be a persuasive theory. But it doesn't.
You can call a donkey a mighty steed, but that doesn't make it so. It is analogous to what we did in Iraq. We bought off insurgence to stop fighting, which only worked until we stopped paying. Its a draining policy that fails the moment the money runs out, which we have seen first hand. It doesn't buy friends, it stalls enemies that will suck you dry then kill you when you are on your knees.
And here we have Roman history being interpreted through the filter of modern politics. Again, if it matched what actually happened to the Roman Empire, it might work... but it doesn't.
That's BS and here's why: We are discussing a possible "new Dark Age" which came about in Europe directly because of the crumbing of the Western Roman Empire, so the comparisons are unavoidable. Since Rome had such a massive influence on European history, as you've said, the greatness of that Empire is always going to be a benchmark by which others judge themselves. America has long been influenced by Greco-Roman culture as is evidenced by our preference for Democracy, which was spurred by Enlightenment thinkers that had "rediscovered" Greco-Roman philosophy, over the Monarchical Feudalism that was still common in Europe at the time of our founding. If the style of the buildings in our Capital aren't an indicator that we've always seen ourselves as some sort of descendant of the Roman Empire, I don't know what does.
What you're calling BS is exactly what I said - ever since Rome, everybody else has always liked to imagine themselves in Rome's image. And yes, that includes stately architecture that imitates classical architecture, Latin mottoes for states and government agencies, yadda yadda yadda. Nothing uniquely American about that, either. The Habsburgs, Napoleon, the British Empire, Tsarist Russia (Tsar means "Caesar," after all), Charlemagne... there's a long tradition in western political ideology of people imagining that their state somehow revives the Roman Empire. Rome casts a very long shadow. But that's propaganda. Tsarist Russia was NOT based on the same structure the Roman Empire was, nor did it face the same challenges. Neither did Napoleonic France. Neither did the British Empire, however much Edward Gibbon tried to make it look that way. Nor does the US. What was "democratic" about the Roman Empire? The analogies do not hold - except in propaganda.