I'm not an expert on Karl Popper, but the whole point of the paradox is that he was trying to reconcile the supposed western freedoms of expression (the so-called open societies) with the fact that it leads to its own contradiction: free speech with no restrictions leads to people freely expressing their freedom-repressing ideas. Some sort of exception needs to be made so this conceptual framework resists scrutiny. So-called closed societies like Cuba or whatever don't have this issue, indeed, they perform the labor of censor. It's just not a good theory of justice at all.
I'm not an expert on Karl Popper, but the whole point of the paradox is that he was trying to reconcile the supposed western freedoms of expression (the so-called open societies) with the fact that it leads to its own contradiction: free speech with no restrictions leads to people freely expressing their freedom-repressing ideas. Some sort of exception needs to be made so this conceptual framework resists scrutiny. So-called closed societies like Cuba or whatever don't have this issue, indeed, they perform the labor of censor. It's just not a good theory of justice at all.