If you are referring to the McCarthy era then a combinations of stupidity, paranoia and a need for self aggrandisement and publicity.
because the communists were doing many not-smart things at the time, and the government thought that if they did something to displease the communists, they would use violence to answer the problem.
The Chinese peasants supported the communists because there current government and leader Jiang did not do anything to help them, and they thought the communists would give them a better life.
The fear was that Communists would dominate the world, or at least most of Asia, Africa and parts of South American and Europe. Communists were thought to be a united international movement.
they thought the communists would end famine
It was the McCarthy era. Politicians wanted to eliminate Communists and thought that adding "under God" would help get rid of or expose Communists. Currently the constitutionality of the words "under God" is being contested.
They feared the Communists would win control.
Communists
He would have supported her for doing what she thought was right.
Capitalism
Mr. Cohn likely wants Miller to change the gangsters to Communists to align the screenplay with the prevailing political climate of the time, where anti-Communist sentiment was strong. By using Communists as antagonists, the story could resonate more with audiences and reflect societal fears, thereby increasing its marketability. Additionally, Cohn may believe that portraying Communists as villains would create a more compelling narrative that taps into the cultural zeitgeist.
Communists
Neither side actually wanted the Berlin Wall. It was seen more as a necessary evil. The Western powers felt confident that eventually the East Berliners would tire of shortages and oppression and rejoin the western world, which is what happened. The Communists thought the Western workers would stand up, throw off their chains and become communists themselves.