I haven't run into any serious economist who believes in the idea, and certainly haven't read any proponents of the idea who are able to justify why this rate is allegedly 5-6 percent higher now than two years ago, or at pretty much any previous point in American history for that matter.
I wouldn't mind talking about this if others are interested. To me, the simplest evidence that this argument is dishonest is that its proponents don't seem to be acting consistently with their beliefs. If they really are right that the natural unemployment rate has risen, any further stimulus or monetary expansion will result in significant inflation which will need to be headed off by the Federal Reserve, and which would permit the organization to divest itself of its fairly risky mortgage-backed securities in the process. And this would be a zero-risk way to drive a stake through the heart of pretty much every left-leaning empiricist out there too....