alt Hacker NewsThere's a <50% chance you'll make money off of it because it's zero-sum, and if insiders make money on average then other traders (i.e., you) have to lose money on average.
The issue is that the odds aren't actually 50/50 on you buying either side of the trade; one half will look like a better deal (and given public information, it is a better deal) so you'll buy that half. Then when the market resolves, it'll turn out that insiders knew some piece of information that made the other half of the trade a better choice.
So then the person who uses public information is actually the bigger fool than someone who uses no information whatsoever and just picks a side of the bet. If insiders know that a volcano is going to erupt and offers a 50/50 payout, people who know the historical improbability will bet that is will NOT erupt, thinking it is an easy payout. But there will be some idiots out there that bet that it will erupt based on dumb luck.