During the 1940s, '50s and '60s, anti-communist organizations in the U.S. sprung up like mushrooms after a rain and fostered a reign of terror. The fears included that of real and imagined commie infiltration—related to everything from suspicion that fluoride was a plot to poison the drinking water, to mental manipulation via the entertainment industry's propaganda agendas—and ultimately led to trepidation that commie moles lurked under beds and in closets.
Had normal people gone completely crazy? Or was there some truth to the Red Scare? Was making people seem crazy part of the grand plan? Remember the canard: Just because someone is, in fact, clinically paranoid, does not mean they are not being followed. And it doubtless is true that in the bowels of American society, communist infiltration into American life was perhaps as real during the Cold War as it was with Putin's hacking during the 2016 election (and probably the 2020 one, too). In the '50s, McCarthyism was so hateful and widespread in its aggressiveness that its toxicity was without equal.
The Red Scare turned America into a culture of shaming (although if you think back to the Salem witch trials, the tendency was in the country's DNA from its earliest European beginnings). People who may have once belonged to "communist front" organizations in their youth or had socialist and leftist leanings became targets of Congress's House UnAmerican Activities Committee (HUAC). Lives were ruined by real or prevaricated associations with the enemy. But policing and investigation was not limited to government. Private, self-appointed watchdog groups were established to provide incriminating data on U.S. citizens. This was a period when poisonous "blacklists" were in force to keep potential undesirables (i.e., progressives and liberals) out of mainstream American life.
One of the most visible, accessible and popular of such lists was a directory of names and affiliations titled Red Channels: The Report of Communist Influence in Radio and Television. It was a guidebook, of sorts, published by the conservative journal Counterattack, that began in 1950 as a book of 151 names of actors, writers, musicians, broadcast journalists and more in Hollywood and New York, accused of being Communist agents provocateurs. The main threats were those in the heart of the entertainment industry, and listing them cost them jobs.

Such lists date back to the 17th century's host of monarchies, as a means of branding a ruler's enemies. An early known American "blacklist" of workers dates to 1774 as a way to deny employment to purported provocateurs in industry. Being branded with this punitive scarlet letter usually resulted in personal and occupational ruin.
In the U.S., the Labor Relations Board Act of 1935 outlawed such lists as a tool for employers. But ultimately, they continued to be used as punishment for a variety of perceived sins—sometimes covert and informal but nonetheless potent. Not only can individuals be marred by their effects, but whole segments of society, from race to religion to gender. What is redlining if not a putative "blacklist" to keep people from buying homes or living in neighborhoods of their own choosing? Shaming and its cousin canceling is a contemporary "blacklist" borne of the social media age. If people are not sensitive to the implications of entities like Red Channels, there is no end to the potential damage.