Do you think billionaires are swimming around in a pool of gold coins or pallets of $100s? Nearly all of the wealth that people are complaining about is on paper. Jeff Bezos owns a bunch of Amazon shares. If you raise the capital gains tax, he'll just never sell those shares. If the capital gains tax was lowered however, he might sell those shares and invest that money in some other endeavor which could create millions of new jobs. I'm betting the guy who created Amazon is a lot smarter than anyone in the government.
Also it would be trivial to game the new cap gain tax law. Do you know how many wealthy U.S. millionaires/billionaires would be running around claiming exactly $999,999 in income on their taxes every year?
All of them.