Agnosticism is an entirely valid stance in situations where there is not enough information. But I do ask for consistency. If someone says, “we don’t have a good basis for making predictions, and therefore I refuse to make one,” then I have no objection. They are being consistent with their agnosticism. If someone says, “we don’t have a good basis for making predictions, so I predict X,” then I object. It looks like the supposed agnosticism is really just an excuse for not having a better justification for the prediction.
By the way, to answer your (presumably rhetorical) question about the stock market: in the stock market crash at the start of the Great Depression, the Dow bottomed at about 89% below the peak. So in fact there was a historical example to use. If you have historical data about a bigger housing bust, I’d be happy to take a look at it. I’m just using the best data I have handy.
