Communism

The reason the red scare existed was because the western capitalists were terrified of the revolution spreading to western Europe and the United States, which was extremely likely in the early 20th century. As such, all manner of censorship of Russian-language news, theoretical texts, reporting, etc. became the norm, and what was deemed acceptable to the capitalists was extremely filtered media, either from opposition in the USSR itself, or from western reporting, complete with what we now recognize as propaganda.

The truth is that the USSR was extremely functional. It delivered consistent results for the working classes, and in so doing doubled life expectancies, brought mass literacy and industrialization, dignified the soviet people, and much more. The west had to rely on a combination of fabrication, exaggeration of real issues, minimization of real successes, and other tried and true methods to invent an alternate reality version of the soviet union. Journalists like Anna Louise Strong, that supported socialism and reported on it honestly, were censored.

The red scare existed because porkie was terrified of a system that stood to steal from under their feet the very foundation they set up for their total reign.