The portrayal of the Communists and Nazis as "twin evils" exaggerates the sins of the Communists in quantity and quality, while minimizing the sins of the Nazis in quantity and quality, in order to show them as relatively equal problems. In other words, its Nazi apologia, and historical revisionism. Read Blackshirts and Reds.

The Nazis executed the Communists, Socialists, gay people, trans people, disabled people, Jewish people, Slavic people, and many, many more. It wasn't simple opposition, it was a racially supremacist ideology.

The Communists executed Tsarists, fascists, and terrorists to the state. They did not create a systematic industrialized murder machine like the Nazis did in order to keep up with how many people they needed to kill.