That would be the "unless it's used as collateral to get real money." part

The problem is that assets have no tangible value until they're actually sold, unless you're going to tax the price it was purchased at every year. But that's an issue because people like Bezos likely didn't buy theirs. I guess you could use the price at market close on the day it was issued

The point of contention comes from not understanding that net worth using unrealized gains is always an estimate.

Bezos doesn't have $240 billion. He has stuff that people think is worth $240 billion. The actual value is imaginary until you find someone willing to pay for it.

Which leads to another issue people don't understand. If Bezos tried to liquidate $240b in stocks, he wouldn't get anywhere near that. Bulk sales like that drop stock prices. Him doing it would probably tank the company.

The best way to try to assign a dollar amount to that imaginary money outside of a sale is when they use it as collateral to get real money.

What amount will be taxed? The assets change value every second the market is open. If you have a hard capture date, then the wealthy will tank their stocks right before.

The best way to tax it is to treat the use of the asset as collateral as a realized gain and tax it as such.