This was true in practice
before technology made communication and synthesized speech trivial. Unfortunately for us all, we no longer live in a world where "more speech is unambiguously better" is true. Technology has ruined the meme of free speech. I'm not saying there are any unambiguously good alternatives; we are all diminished by its loss. But clinging to its corpse isn't doing anyone any good.
As for the Churchill quote, the reason that democracy has those qualities is because it inherently involves compromise. An uncompromising philosophy like "more speech is always better" is quite a different thing. We need a new rallying cry to replace the meme of free speech, probably something to do with the notion of signal:noise ratios, but it's beyond me to invent such a meme.