Isn't the control group the part of the graph from 1993-2000ish, where perception and reality are fairly closely correlated?

I guess that raises more questions than it answers. What about the rise of cable news? That tracks the change in the graph more closely than the rise of social networks. What about 9/11 and the war on terrorism? A significant portion of the US population lost their shit and never got it back. I'm not sure we should pin all or even most of the change on social media.

I think you have a point that the "good old days fallacy" has been around since forever. But it also seems like something dramatically changed 15 years ago or so.