Prediction markets are just inside traders profiting off gambling addicts. If you are not an inside trader, you're the loser paying out.
But once they get big enough to attract the attention of people that directly affect the outcomes they will eventually become useless because people will realize the only options are to have inside information or be willing to hand money over with inside info.
The only “fair” outcomes will be things outside human control, like betting on the weather.
And even on markets where someone would benefit from inside information... insiders leak a lot more information than you'd think before it tends to hit the market. Even reading the news can tell you more than you'd think if you look at it right. The single biggest hint is "Why am I reading this, and why now?". News stories on geopolitics almost never arise naturally, and that question will get you to a LOT of information that was not explicitly stated.