Insider trading drives prices closer to fair value. A CEO dumping shares before reporting a bad quarter saved money for unknowing purchasers buying the stock. If the CEO buys shares before reporting a huge new government contract, they get a better price for clueless sellers.

Now public companies could still restrict CEOs and other employees from profiting from insider knowledge. It could even be as simple as requiring employees to file disclosure filings before any stock transaction to level thevplayomg field.