Really, it all boils down to those last 2 paragraphs I wrote.

Would it have made a difference in the Soviet Union, if their Constitution said "the Supreme Soviet shall not abridge the right to free speech"?

Or rather, operating with the political system that they did, would they have instead simply found an escape clause to justify ignoring that and heard not a word of protest from any of the factions with real power, who all had a vested interest in the people shutting their traps?