It is important to note two things. The first is that as always, the news media repeated and amplified McCarthy's lies merely because they were sensationalistic and thus grabbed eyeballs and thereby generated lovely revenues for the news organizations in question. These news organizations didn't care about the fact they were corroding society; they only cared about generating revenue. Today, the situation is even worse - now many simply tell lies directly and invent "facts" to draw in gullible audiences.

The second is that today, people who follow demagogues live in an alternate reality made possible by Internet echo-chambers, which means that reality has no purchase on their beliefs. Thus charlatans and blustering halfwits can dramatically extent their effective political lifespans simply because their followers are incapable of interacting with the real world.

So the real lesson learned is that we're in a much more precarious situation than ever was possible in the McCarthy era.