There's always been people who believe in nonsense. Most people, throughout most of history have. The meaning of "post-truth" today is that people in power are no longer being asked to justify what they do on the basis of fact. (It doesn't mean that facts don't exist or that they don't matter, I just found it off-putting that you'd try to suggest that.)
Allow me to paraphrase a concept from Tolkien: evil doesn't win because it's a superior force, it wins because it convinces you that it's already won. "Look over there, evil wins. Look here, evil already won. Evil always wins, that's the way it has always been. You can't fight it so give up."
You can't win by spreading evil's messages, even sarcastically. You win by being a superior force and never giving up. People's credibility should actually suffer when they do or say things that are incredible, and people who appeal to us with facts and compassion should be rewarded.