Part of the reason for the 1st amendment to the U.S. Constitution was the presumption that good information would conquer bad in the 'marketplace of ideas'. Do you believe that the Earth is round? Or that the Earth orbits the sun? With freedom of speech, you could advocate those ideas and, it was hoped, overcome the flat-earth and geocentric hypotheses.
Then we had superstition, urban myths, and fake news.
Perhaps the truth-will-prevail folks failed to account for some important factors:
1) While people might have limited time to spread falsehoods, computers have overcome that.
2) Controversy sells, particularly in the age of click-advertising.
3) While charlatans used to be identified and shunned, internet anonymity lets them persist and reincarnate themselves.
4) No idea, no matter how bad, ever seems to go away entirely; convincing 'most people' is the best you can do.
5) Many people prefer a falsehood that seems to make them happy to an unpleasant truth.
Is free speech a failed experiment in the service of truth?