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.