Communism causes Stasi. It can hardly co-exist with other political ideologies! It seeks to eradicate them and institute a one-party state. One can hardly do something like this when right-wingers are allowed free speech right alongside the good people. Thus, the state needs to defend itself - for everyone's own good, of course.
"You are dictatorial." My dear sirs, you are right, that is just what we are. All the experience the Chinese people have accumulated through several decades teaches us to enforce the people's democratic dictatorship, that is, to deprive the reactionaries of the right to speak and let the people alone have that right.
-- Mao Zedong
They are strange creatures, these Bolsheviks. They talk of freedom and the reconciliation of the peoples of the world, of peace and unity, and withal they are said to be the most cruel tyrants history has ever known. They are simply exterminating the bourgeoisie, and their arguments are machine-guns and the gallows. My talk to-day with Joffe has shown me that these people are not honest, and in falsity surpass all that cunning diplomacy has been accused of, for to oppress decent citizens in this fashion and then talk at the same time of the universal blessing of freedom - it is sheer lying.
-- Count Ottokar Czernin, Former Austro-Hungarian Minister of Foreign Affairs, "In the World War" (1920)
"In comparison to conditions imposed by U.S. tyranny and violence, East Europe under Russian rule was practically a paradise."
-- Noam Chomsky