As I recall, in 1995 there was a book released about something called "The Venona Project". It seems that during WWII and in the post-war era there a US code-breaking effort that was able to decode at least some of the Soviet Union's diplomatic/intellegence codes and cables from their embassy to Moscow. Many members of the media were found to have been Soviet agents as well as many American Communists in various bureaucratic and even military posts in Washington.
And yes, Sen. McCarthy's claim were mostly proven correct. As were his fears that these Communists were spying for the USSR. But many in the media were and still are committed to overturning our Constitution. So they keep the lies alive.
And since they had the media since the 30's thru the 70's (and a lot of it even now) the "social momentum" has encouraged Republicans and conservatives to "go along" with the myth of "McCarthyism".
The only hope to keep bringing up the truth whenever possible, like here in TH.