Are you saying the "sector of betting on shit that can clearly be insider-traded" is illegal? Does that include like gold and S&P500?
The way I see it, prediction markets' main function is to connect gamblers with insiders posessing useful information. Are you concerned for the gamblers losing? But they were gonna lose anyway, one way or the other. Or are you concerned about the insiders winning? Sucks, but at least the public gets information by way of the prediction market being more accurate.