It's the dialectic. The bad "dictatorship of the bourgeoisie" must be replaced by the good "dictatorship of the proletariat." The "dictatorship of the proletariat" will be just as tyrannical and merciless as the "dictatorship of the bourgeoisie," but the important thing is that the right people will be doing it, so it's okay.
The Left is the "thesis of history." The Right is the "antithesis." Everything is permitted for the former (so that it may perform its "historic mission"). Those same things are forbidden to the latter because they're "the bad guys."
Rights exist only for the thesis. The antithesis has no rights.
Ha! So true.