Can a nation-state be collectively evil, and can we regard them as irrational actors if that assessment is made? Was Imperial Spain evil? Was Imperial Rome evil? Was the British Empire evil? What about China? What about America? Does our history of chattel slavery make us 'evil', and does that make us irrational? At what point does a polity cease or begin to be 'evil'?
The realist answer to all of those questions, and to yours about the Soviets, is no. You ignore that the Soviet government also industrialized their economy in a relative blink of an eye, won equal rights for women, and destroyed an incredibly oppressive aristocracy. If you only focus on America's bad points (they destroyed dozens of native civilizations, they engaged in brutal chattel slavery, and they systematically oppressed black people and attempted to subject them to eugenics) we look pretty evil. Hell, the injection of human test subjects with syphilis without their knowledge, and then observing the subject without treatment is horrific, but that's not reflective of the whole of our society. Any categorization of any country or ethnic group as 'evil' is just emotion talking over reason. It's a marvellous propaganda tool, but it's damaging in the field of international relations, where cooler heads must prevails. Russia has always been geographically predestined towards autocracy, and that isn't going to change any time soon. Understanding why they behave in the way that they do makes them predictable and gives us an advantage on the world stage. Pretending that there's some mystical sense of evil involved just fogs up our glasses, so to speak.
