My only remaining qualm about taxing the shit out of rich people is the argument that if we do, they'll just move somewhere else. How do you counter that?
I'm sorry but you can't cander to the whims of rich people, if they want to move to avoid taxes, there is little we can do, in either case we lose the money, either by letting them go or letting them pay lower taxes. Getting rid of citizenship is at least a little bit of a deterrent for these people, I remember in France doing it worked somewhat to prevent these kind of shenanigans when they increased their taxes.
At the end of the day to, where are they going to go? No matter where they go, eventually the people around them will increase their taxes unless they move to like a 3rd world nation, which which case taxes are the least of their worries.
not everyone will be uniformly willing to leave the country where all their business interests are, as well as where they grew up and have lived etc. there was no mass exodus in the 1950s when marginal tax rates were very high.