[throw_nbvc1234]

A "good" prediction market is when it functions as an accountability market. The insider trading problem isn't an issue if the outcome is for a greater good. The problem is that money is the easiest way to ensure anonymous predictors are serious about their predictions and getting richer is not a greater good. If you were to require politicians to participate in a reputational prediction market, the aligned incentives might make it a positive thing.

You could let ordinary people piggy back participate too, and then use the results to filter through internet/media noise but that starts to smell too social score-ish.