This is a rediculous ahistorical argument.

The Roman empire did not collapse right after Hadrian. Indeed, the next two emperors after Hadrian are often called "good emperors" (Antoninus Pius and Marcus Aurelius), and Rome was quite strong then. I don't know of anyone else who seriously claims that building the border walls in any way led to the collapse of the Roman Empire. Indeed, the fortifications were specifically designed to make the empire easier to defend, and given what happened afterwards, there's decent evidence that these fortifications did help in the empire's defense.

Anyone interested in the history of the western Roman empire would be well-served to listen to the excellent "History of Rome" podcast by Mike Duncan: https://thehistoryofrome.typepad.com/ For this purpose, you should listen to episode #179 ("The End") at https://thehistoryofrome.typepad.com/the_history_of_rome/201... . Duncan says that there isn't just one cause of the fall of the western Roman empire - instead, they were overwhelmed by a confluence of multiple factors. Duncan says, "The decline and fall... is not going to be able to be explained away by 1 or 2 simple causes... (each of the many problems) played off other in a synergistic orgy of destruction". Episode #179 discusses this in more detail. Indeed, there were efforts near the end that might have saved it.

The real issues are complicated and don't easily fit into a "left" or "right" discussion. If anything, the beginning of the end was that the border walls were penetrated, not that border walls were built, so you could argue that the border walls were necessary to have allowed the empire to have lasted as long as it did. On the other hand, part of the reason they were penetrated was because the Romans didn't let the Germans have real power within their empire and didn't do a good job integrating Germans into their empire. On the gripping hand, in many ways the collapse was in part because Rome had become accustomed to fielding armies by paying mercenaries who were loyal only to their commanders, instead of having soldiers who saw themselves as Roman citizens fighting for the Roman government... and as Duncan notes, paying off an 'other' to not invade is not a lasting solution. ("The empire was no longer able to raise a national army, it could only pay for protection. And this, I can assure you, is an unsustainable model of self-defense.")

And of course, only the western Roman empire fell in 476; the eastern Roman empire continued for about another thousand years.

I'll add my own viewpoint. One of the biggest problems of Roman empire as a whole (compared to the previous republic) was its failure to have a way to peacefully select the next ruler. This lack of legitimacy led to occasional outbreaks of civil war that repeatedly sapped Roman strength. I think that is a key problem that led to the fall of the western Roman empire when it did. The eastern Roman empire had same problem as well. For example, legitimacy issues in the eastern Roman empire led to serious problems after Basil II, and their civil wars fatally weakened them.

There are definitely lessons to be learned from Rome (and history in general), but that requires more careful examination of what actually happened.