Here's Otto Friedrich on John Howard Lawson, the first member of the Hollywood 10 to speak before HUAC, and a playwright before his Hollywood days:

Lawson's second Broadway production, Processional (1925), brought him success at the age of thirty. Subsequent titles tell a story: Loud Speaker (1927), The International (1928), Success Story (1932). Success lured him west, as it lured so many others, and the Hollywood titles began to tell a different story: Dream of Love (1928), Our Blushing Brides (1930), Bachelor Apartment (1931), Success at Any Price (1934) ...

He was the first president of the Screen Writers Guild, and he made no secret of his ideological views. Writing in New Theatre magazine in 1934, he announced that he had joined the Communist Party, and he added, “I do not hesitate to say that it is my aim to present the Communist position.” There was something sad about Lawson's efforts to “present the Communist position” on the screen. In 1938, the same year in which he wrote Algiers to introduce Hedy Lamarr, he also wrote Blockade, Walter Wanger's account of the Spanish civil war, which somehow failed to say which side was which. “This I accepted because it was the only way in which the picture could be undertaken,” Lawson said.

Not only did it fail to say which side was which, it failed to mention which country they were in, or that it was even a civil war; it actually seems like a war between different countries. So the great Hollywood movie about the Spanish Civil War that was made during the Spanish Civil War doesn't mention either “Spain” or “civil war.” 

In a few grafs, Friedrich lays out the absurdity of the HUAC attacks. HUAC says it was concerned with communist infiltration of Hollywood and the messages these spies were lacing into movies. And yes, there were communists in Hollywood in the 1930s and '40s. But even the most vocal of them, given a dream project, still produced pablum.

The Coen brothers played off this nicely in “Hail, Caesar!”