We can further break down the Victim class from MaybeDefensible into three sub-classes: 1) cataclysmic events, e.g. a meteor hits NYC, 2) minor negative or positive events, e.g. meteor hits cow, or cow has twins, and 3) wondrous events, e.g. a cure for all cancers.

Cataclysmic events are not great prediction market events because if you put enough money against them, someone's going to find a way to throw a meteor at NYC. And minor events have limited impact, so not many people will be interested in them.

Wondrous events seem to work well because most of the money will stack against an all-cancer cure, and we don't care that the inventor(s) could win big because society wins way much more.