>This all sounds good, but if I assert that the earth is flat on Facebook why shouldn't that simply be labelled false so others can avoid wasting their time trying to refute a ridiculous assertion?

The issue is I don't agree with all that. Who cares if crazies share flat earth theories on Facebook? You either trust your fellow humans to be able to think critically, or you don't. And if you don't, then why do you trust them with power of life and death over you via the state and voting?