> Retail investors should be index funds anyway.

That does does not solve the problem as insider traders will still be shifting profit to themselves. You still need non-insiders (not necessarily retail investors) to make the market work - even for insider trading to work you need a non-insider to trade with.

> Until fairly recently there was no 'insider trading' you could get in trouble for in commodities in the US. That hasn't stopped non-insiders from trading in commodities.

Can you show that it had no impact on how non-insiders traded? How recently was recently?

> Also, even if insider trading is legal, that doesn't mean your company needs to allow it: you can still punish your own employees for it, and eg claw back bonuses and sue for breach of contract and breach of fiduciary duty.

A lot less of a deterrent, and a lot of people with access to inside information have a lot more to gain than to lose.

> In any case, American insider trading regulation is already laxer than French insider trading law. And it doesn't look like French companies have an easier time raising capital.

Both do have insider trading laws so both are probably good enough, and there are a lot of other variables.