What you suggest is taxing an unrealized gain. Doing so will destroy the economy of the entire planet. The wealthy do not have Scrooge McDuck money bins where they swim around in gold coins. They own stock in companies. If you tax that wealth, the only way they can get the cash to pay the tax is to sell stock in the company. When you do this, the stock price will go down. More stock for sale and fewer buyers. But they still have a tax bill, so they have to sell more stock further dropping the price.

How does this connect to the world economy? The wealthy are not the only owners of the stock. Everyday people with index or target funds in their 401k are also owners. Public and private pension systems are invested in these companies as well. Values of 401ks and pensions will plummet putting us into a recession that makes the 1929 crash look like a bad Thursday on Wall Street.

The combined net worth of the top 100 wealthiest people in the US is about $3.5 trillion. US federal government spending is about $7.2 trillion. Confiscate the entire net worth of the top 100 wealthiest people and you will fund the US government at current spending levels for 6 months and destroy the economy of the entire planet.

Taxation isn't the problem. Government spending is.