The remedy for speech that is false is speech that is true. This is the ordinary course in a free society. The response to the unreasoned is the rational; to the uninformed, the enlightened; to the straight-out lie, the simple truth.
When I was eight or nine, there was a very scary case of a guy who murdered four children in my community. I had no conscious memory of it, but now I'm sure that we all must have felt for these kids. We must have felt it, but no one was saying anything. I wonder now how much that impacted on me with