[Nevermark]

Exactly! Reselling at a better estimates of real value make a market more efficient.

In two ways. The immediate is when they buy or sell a miss-priced asset, the other side of the trade benefits from a slightly more accurate price.

Then the market as a whole benefits from reduced risk, as the miss-pricing gets reduced. Whether or not each individual buys, sells, or abstained based on the more accurate valuation.

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The problem with insiders isn’t that they have unique information on miss-pricing, and are trading on it.

It is that, one, if they are allowed to trade on miss-pricing they are highly incentivized to create it.

And two, they are leveraging the shareholder’s property, the company’s private information, against the shareholders. Despite insiders only having been been given access to that information, explicitly or opportunistically, in order to provide benefits to the shareholders.