There are arguments about wealth taxes inducing capital flight and investment disincentives, the difficulty of paying tax bills from illiquid intangible wealth or even quantifying it, and whether it's really a good thing to pressure people building a company to sell much of it off, but telling income tax payers that an effective tax rate of 20% is high isn't one of them...
This is untrue btw
50% of people in the US pay effectively no net taxes
Billionaires included, defence contracts and corporate subsidies count just as much as food stamps.
If the US and the EU introduced a wealth tax then it would be relatively difficult for the capital flight fears to materialise. But yeah, the trouble with wealth taxes is that wealth (i.e. capital) is mobile.
Which is why land and property taxes are probably the most effective way of taxing wealth.
We have societal problems around food costs, housing costs, healthcare costs, &c; but people with extreme wealth are not bidding up sandwiches, studio apartments, &c, &c. If we "solve" their wealth by taking it from them and giving it to the government, what does that help? What good is the government going to do with that? Allocating money through the government has not been a particularly successful strategy for improving the overall standard of living.
That's how you end up with an over-regulated country where people doing great things for the country's economy start choosing a different country to build their dreams in.
It's also how you drive the currently-wealthy to other countries to spend and invest their fortunes in.
The possibility of being ultra-wealthy is a huge reason to build awesome shit in the US that creates millions of jobs and brings the US economy ahead.