I don't think you've read any of the histories of the era. Contrary to what many people would like you to believe, there were actual Communists in Hollywood.
Old news, the video's already 3 years old but a reminder of Hollywood's perennial leftism is always good. Razorfist is a conservative-leaning youtuber who also streams, puts out vids on current events, occasionally does videos on metal bands, noir movies, battletech and other assorted topics. Definitely worth a look!
Sources cited in video:
Albert Maltz - 'What Shall We Ask of Writers?'
https://www.unz.com/print/NewMasses-1946feb12-00019
'Darkness at Noon'
https://libcom.org/files/[Arthur_Koestler]_Darkness_at_Noon.pdf
'The God That Failed'
https://archive.org/details/in.ernet.dli.2015.185523/page/n19/mode/2up?view=theater
'Hollywood Party' by Kenneth Lloyd Billingsley
https://www.amazon.com/Hollywood-Party-Communism-American-Industry/dp/0761513760
I guess they considered a Communist takeover of mass media as a danger to national security.
(By the way, the studio bosses were also annoyed at many of their "politically engaged" writers, who kept trying to slip "Communist themes" into mainstream movies. Basically, what they termed "conscience movies" was code for "Communist-friendly" themes. And these usually aimed to discredit American culture and society. Such "conscience movies" dwelt on racial inequality, the evil of Europeans in their dealings with Native Americans, etc. Hollywood producer Irving Thalberg was driven crazy by writers that he knew to be Bolshevik-sympathizers, and he started trying to root them out even before Congress' House Un-American Activities campaign.)
You can read a book on it entitled "Hollywood Party," by Kenneth Billingsley: http://www.amazon.com/Hollywood-Party-Communism-American-Industry/dp/0761513760
A lot of these writers were influenced by a group of Marxists called "The Frankfurt School". Back in Europe, these intellectuals were called the Karl Marx School of Economics. Once they fled to America, they set up camp and decided to infiltrate American academia and condition the youth with pro-socialist messages. One of their main tacticians, Herbert Marcuse, was the first to write about the importance of "speech codes" on campus in the 1930s. It's what we today call "Political Correctness". Marcuse said that it was essential NOT to allow a free debate (lest the Marxists lose). So certain words and concepts had to be censored from people's minds. If you could promote self-censorship among the youth, then you stood a better chance of winning. (One of the main censored topics was the body-count of their beloved socialist utopias. This was not ever allowed to enter into a discussion of the subject. Otherwise, Communism might not look as appealing and their side risked losing the "hearts and minds".) . . . . At any rate, their main goal was to discredit American culture and persuade the youth that a collapse of the traditional America was desirable. To inculcate them with self-hate in order to destroy the nation from within. Because of this the Frankfurt School dwelt on none of the good things about America, but all of the bad things. The West, for instance, is the only society on Earth to formally ban slavery. The slave trade is still going strong in Africa and in Muslim nations. But the Frankfurt School doesn't want that discussed. The West [the only culture that ever banned it] was framed erroneously as the only culture to ever engage in it. Cultures that had slaves prior to the West (and continued to have slaves) were edited out of the debate. So a false picture emerged. A culture that spilled blood to end the evil practice was now re-framed as the only bad guys. In addition, white people who were slaves [like the Irish, or Slavs in the Ottoman Empire (where the term "slave" comes from)] were edited out of the debate, as well. A new picture had to emerge. The West = bad, Developing Nation [which still owned slaves] = good.
Here's the presentation on them: https://www.youtube.com/watch?v=q6c_dinY3fM
https://www.amazon.com/Hollywood-Party-Communism-American-Industry/dp/0761513760
McCarthy and his committee uncovered a network of communists within the government. That's a fact. Your entire characterization of him is ripped straight from communist propaganda that was then pushed by sympathizers in various formats and persists to this day.