The original question was about entertainment blacklisting, which was a completely different thing from the espionage and State Department intrigue you're talking about. No actors were passing atomic secrets to the Soviet Union, nor were they ever in any position to do so, and nobody ever alleged that they were. I own an original copy of Red Channels -- a book published by an ultra-right-wing organization, and which was never sold or distributed to the general public -- and 99 percent of the accusations are along the lines of "Joe Actor signed a petition for the integration of baseball in 1944." There are exactly three people in the book who are flat-out identified as members of the Communist Party -- Pete Seeger, Lillian Hellman, and Dashiell Hammett -- and all the rest are just smeary innuendo. Aware Inc., which took it upon itself to enforce "Red Channels," was, to be blunt, a crude shakedown racket perpetrated by a cashiered FBI agent, an ad agency flunky, and a paranoid supermarket-chain executive from Syracuse -- actors would be listed on the flimsiest of pretenses and then charged a fee to be "cleared." Failure to pay up meant pressure on sponsors -- backed up by threats to remove their products from stores under the executive's control -- and these sponsors, in turn, brought pressure on networks and production companies to get rid of the personalities cited. That's all "blacklisting" was. There were no "investigations," there were no legal charges, there was nothing but simple, filthy extortion.
The average American had little to no idea this was going on in show business to the extent it was -- because the industry was very careful to avoid publicly accusing anyone of being a Communist for fear of courting legal action. It was John Henry Faulk's lawsuit against Aware, Inc. in 1957 which finally dragged all of what was going on into the public spotlight and exposed it as the paranoid fraud that it was.
The Rosenbergs and Alger Hiss were not "blacklisted." They were arrested, charged with Federal crimes, and convicted in open court on the basis of hard evidence. That's a big, big difference from the closed-door, star-chamber tactics used in the entertainment industry to throw Joe Actor out of work because a couple of crackpots in Syracuse claimed that someone who looked like him was seen reading the Daily Worker on the subway in 1936.