> For instance, I'm in favor of bets that a certain astroid will strike the earth at a certain time and place. A signal from the prediction markets might cause somebody to evacuate in a scenario where they'd otherwise cry "fake news."

I understand the point you're making, but in this case, you're still incentivizing someone somewhere to not attempt to the best of their ability to intervene in that astroid. Bets that truly can't cause any change in behavior that might affect the outcome are a mostly theoretical category, in my opinion.