As a former user of in-trade and more recently of poly market, it is so annoying that there are laws against these sites. They serve an incredibly important function: letting people learn what’s happening in the world around us by observing a single number (e.g. % win probability). I most receently used the site yesterday to see what the incumbent Australian government’s reelection chances are after they tabled ‘ID a…
I think that phrasing is a bit too optimistic. Even in cases where the "prediction" cannot influence the outcome, the primary "learning about the world" involves the imputed opinions of bettors.
Betting at horse-races doesn't teach you nearly as much about horses as actually going to the stables. :P