Revolutionary leftism
is a kind of authoritarianism.
The mainstream view of HUAC and the Red Scare is, in my opinion, extremely biased. HUAC investigated all kinds of subversive organizations, including German sympathizers during WWI and the German-American Bund during WWII.
HUAC acted purely as an investigative body and didn't have (and, per the Constitution, never had) the legislative power to blacklist people from working in any given career. The expectation was that HUAC would carry out the investigations to bring information to the public light. The studio executives who acted on the information discovered were doing so of their own volition; HUAC had no real power to compel them to do anything in particular.
House committees investigate things all the time, too; even things that are purely in the domain of the public sector. For instance, in 2005 a House committee investigated steroid use in baseball. And, largely as a result, Mark McGuire, who refused to testify, has never been elected to the Hall of Fame. Are the Hall of Fame electors "basically government proxies"?
It's also a matter of historical fact that most, if not all, of the "Hollywood Ten" were, in fact, members of the Communist Party USA, which as another matter of historical fact, was directly bankrolled and controlled from Moscow. In other words, the Hollywood Ten were, albeit indirectly, under the influence of Joseph Stalin.
If a Congressional investigation today discovered that ten screenwriters and filmmakers were members of a secretive racist organization under the control of a hostile foreign power, they would be immediately blacklisted by their private employers, and everyone would support that. Just as, if the owner of a basketball team were discovered to make racist comments in private to his own girlfriend, he would be immediately blacklisted from the league and forced to sell the team to Steve Ballmer and everyone would think this was OK.
Well, for a brief moment in American history, people figured that being a Stalinist was just as bad as people today think making racist remarks to your girlfriend or using steroids to break the home run record is, and reacted in exactly the same way.