One - you would not knowingly trade with someone who has fundamentally more information than you, so there would be ver y little demand for equities that can be

One - you would not knowingly trade with someone who has fundamentally more information than you, so there would be ver y little demand for equities that can be traded by insiders. Two - there would be absolutely no way to prove in most cases, one way or the other if the 'insiders activity' was damaging or not for the company. For example, a bunch of insiders discover something disastrous and start selling cheap, sending a panic into the value of the stock. Is this 'bad for the company'? Or not? Then the 'problem' turns out to be not such a big deal, and they buy back on the cheap. Was this damaging to investors? Even if the insiders were acting legitimately, i.e. selling when something was wrong, buying when it was not ... it would 100% not be in the best interests of other investors - you see from this example that the very nature of 'insider information' makes 100% of trades by insiders 'not in the interests of other investors'. "as evidenced by the size of other markets that lack insider trading laws, like real estate, commodities or cryptocurrency This is wrong. Real estate can generally be independently valued. That's why it's required by law in many countries to have 'independent' assessments of a home's value. Same can be done with commercial. In commodities and currency there are no 'insiders'. There's nothing built into the price but the inherent value of the commodity itself. Corn is corn is corn. Insider trading would definitely apply to a big agri-business, but for corn futures, or USD or even Bitcoin - there literally are no 'insiders'.There are 'insiders' in companies, but a market does not have insiders. Just intelligent people researching, analyzing, with their fingers on the pulse. Demand for stocks would dwindle to nothing without insider trading laws, that's why they exist in every developed market.