If widely sanctioned instead of largely banned, insider trading by company leaders and decisionmakers. The leaders would be incentivized to make decisions that preference their own interests rather than the interests of the company as a whole. Putting gypsum in with the flour to report better margins, that sort of thing.
I think that that ownership by a diverse group of non-insiders is preferable to consolidating the control over huge individual insider shareholders, for two reasons:
- That ordinary citizens can be shareholders of companies, and so won't make decisions against their own interests.
- That large groups tend to be more ethically moderated (in the nuclear physics sense: slowed down from snap decisions) and less likely to become cynically corrupt than individuals.
Now, big groups still do those things all the time, but the idea is that, for a few reasons (e.g. people don't corrupt at the same rates, so the unless the group shifts all at once they'll identify the people that become corrupt as interlopers and outgroup them), it's still better than taking the chance on an individual.