Assuming that you are in cash or another asset class that isn't being sold off.

No need for that assumption. Equities going down is not a problem for reasonable investors. You just buy more for cheaper prices according to your schedule and wait. You still own the % of your companies. It's not worth less just because you can't temporarily sell it. It would be like saying that price of your house is fluctuating from 0 to 500k depending if there is a potential buyer today or not.

Stock market crash is only a big problem for leveraged over commited entities, very small inconvenience for people beyond accumulation phase (as they may need to sell very small % of assets in coming months) and huge opportunity for everyone else.

Stocks crashing is fantastic for a little guy. It's the same with real estate prices and it's the reason entrenched players do everything to prevent it.

Or just that you have some kind of disposable income.

Sell, what exactly? They won't buy after that?

It's hard to know exactly what the repercussions were, but in my experience a lot of stocks were down yesterday, including some FAANG's and the like down 5-10%. Those numbers aren't likely to be permanent, so anyone who wanted to buy anyways got a 5-10% discount.