Do nothing. Point it out now and again I guess. Either a) most people are smart enough not to believe the first thing they read on the internet, or b) the Russians and Chinese are right and democracy is a farcical sham for a people that's too dumb to rule itself. In either case, doing nothing is appropriate. Actually, this dichotomy goes for most "free speech" debates. If you have to protect the citizenry from its own stupidity, you should probably reconsider this whole "voting" thing.