The standard line for years has been that there was nothing to the Hollywood Communist Party. Portrayals like The Majestic and The Front imply that many people implicated were not even really communists. They just joined to impress a girlfriend. Recently Sean Penn complained about his father's treatment during the period.
While it is true that this organization was ultimately infective, it is also true that they really were hard-core communists who were plotting to overthrow the US government.
After the fall of the Soviet Union, there was a period when the Soviet archives were publicly available. Several historians traveled to Russia and went through them.
There were actually three different communist parties at the time. The communist party of California and of Los Angeles were harmless and open to anyone who wanted to join.
The Communist Party of Hollywood was a different animal. They literally took their marching orders from Moscow. You did not join to impress a girl. There was a screening process set up to weed out all but the truly committed and the final decision on who was admitted came from Moscow.
Once you were in, you surrendered much of your personal freedom to the party and to Moscow. You could only marry a fellow communist. Similarly, if you had an analyst or psychiatrist, he had to be approved in case you gave away any secrets.
It is tempting to give this group a pass. After all, their side lost so they did not cause any real harm. But it is important to put it in perspective. During the 1950s, communism was advancing. During the 1950s and 1960s communism took over a good bit of the world. India and Egypt were both socialist. Revolutions were taking place all over Africa and South America. Half of Europe was occupied by Soviet troops. There was genuine cause for alarm.
To give a modern parallel, they were similar to the modern groups that plot to commit acts of terrorism in the US. They were not nice people and they were not innocent.