Laffer Curve. Depends on the country but France for example already takes 44% of their GDP as tax, runs heavy deficits, and attempts to make up the difference by increasing taxes on the wealthy causes them to leave.

At some point they'll need to do austerity.

It's well-established that Americans are much earlier on the curve than wealthy people would like to believe. Mamdani Doctrine: ignore the part of your brain screaming rich people double consciousness and just do what's right for and fair for most people. At this point in history, that's taxing wealthy people - including paid-off-6k-sq-ft-house-with-2-people-in-it pensioners and $200k-a-year-living-paycheck-to-paycheck-in-a-coastal-metro yuppies. Yes, there'll have to be some tough decisions; austerity, indeed.