The "marketplace of ideas" was always a flawed metaphor. Ideas don't compete on merit; they compete on memetic fitness—how easily they spread, how good they make believers feel, and how effectively they suppress competing ideas.
@Daojoan yep, every time I hear that phrase I think "you just basically want your idea to win and you gonna do all to get there, actual validity be damned". People who need to argue for ideas usually try to skim around fact they don't like current best one.
@DrorBedrack@Daojoan Regardless of one's views on your philosophical tangent, you've basically turned the OP's message 180° from what it was saying.
It's not that "truth"/validity doesn't matter, but that having a "marketplaces" is utterly the worst way to foster it, because the evolutionary pressures reward "memetic fitness" not "truth".
Same reason why ascribing moral goodness or desirability to Darwinism in other contexts (biological systems, social systems, etc.) rather than treating it as an adversarial property that's amoral is so bad.
@dalias I went on a tangent, that's like, 90⁰, at best. Isn't OP's message that ideas win in a darwinian struggle? After all, "memes" were originaly the "genes" of ideas.
@DrorBedrack No, it's that the ideas that win in a darwinian struggle are not the ones that are "true", "good", or accurately reflect reality in ways that let the people who hold them make good decisions. They're the ones that have the best reproductive success as ideas. Not as agents of success for the organisms that hold them, but as parasites infecting those organisms.