We know that a polygraph does not work, but how do we know that this won't work without real-world data?

And nobody is being accused of anything, there is no burden of proof involved yet. If you mean that we can't subject someone to a lie detector while asking questions, i.e. we cannot subject anyone to anything without a reasonable suspicion, then we couldn't have airport security at all unless someone tweeted "today's plane is gonna be da bomb!"

Which would be a lot better than the current state of things in the USA, but that's not how this works.