It is not a free market if there is insider trading. If insiders are trading other market participants are by definition getting screwed by what was advertised as a fair, impartial system.
You certainly wouldn't participate in a market where you did not think you had fair odds. Tho maybe you're inclined towards the rigging side of things.
Finally, since you're trying to work the information angle, would you care to share any legitimately meaninful information you've gained from prediction markets?