If you're not trading overnight and there's a flash crash that corrects itself overnight... it's the people who are trading overnight taking money from each other.
Most Americans who invest money don't trade at all. They pay some guy at a bank to do it, and the guy at the bank is exactly the kind of guy who is trading at 3am.
Most people are in simple retirement year funds which have a set algorithm which decides by simply rebalancing to follow an index and appropriately mitigating risk by shifting some assets towards bonds.
There is no one trading on a whimsy. The mutual fund founding documents specify an exact time of day (or times) at which the fund gets rebalanced and it simply follows the algorithm..
The price shocks discussed here will not affect that
