The error is to assume that there is wealth to tax. Imagine an island with 3 people, which produces 2 burgers a day, so the poorest one can't get a burger. Now the government taxes the richest person, and buys one burger. who lost the burger?
The burger is taken from the poorest person that was able to buy a burger. Now you have 2 people who cannot buy a burger.
This is why you cannot tax unrealized gains. You are sacking the poorest. Is not matter of how the government gets the money. The problem is that the government spends the money.
The poorest always pay all government spending. Always.