A common argument in philosophy is that bad ideas should occur in the open - where everyone may ridicule them. When they are cast to the shadows they can grow, under everyone's noses, in private where only there are they allowed to exist. In private, these bad ideas cannot be challenged by others and people will be convinced to believe in them, with nobody challenging the idea as a genuinely terrible idea. It gives b…
That common argument rests on norms established by millennia of relatively difficult communication. Best not to assume that the same people would come to the same conclusions today. For example, QAnon believers have not had their speech restricted. That conspiracy theory is as open as anything you could name. People have challenged it. It's still going. If you believe that challenging terrible ideas makes those who h…
It doesn't make them go away. It allows them to be refuted - which hopefully stems at least some of the indoctrination that would otherwise occur only in private.
If everyone I've ever known tells me vaccines are evil and I never am told or shown otherwise - I'll grow up continuing to think vaccines are evil. If you refuse to let me speak about vaccines that only further proves that you're evil and trying to hide the truth - and strengthens my indoctrination. Now, poor arguments against anti-vaccers also serve to strength the indoctrination so there's some bad with the good... (Also just to be certain on things: "you" and "I" are used generically for easier writing, I support and believe in vaccines.)
There are also plenty of bad ideas that do die to public scrutiny - think of anytime anyone has ever been talked out of "doing something stupid" because they shared what they had planned to do.