Three basic options. Choose wisely, lest you go totally insane
There are three basic ways to talk to complete idiots.
The first is to assail them with facts, truths, scientific data, the commonsensical obviousness of it all. You do this in the very reasonable expectation that it will nudge them away from the ledge of their more ridiculous and paranoid misconceptions because, well, they're facts, after all, and who can dispute those?