> ... even if paying a wealth tax forces stock liquidations that cause stock prices to plummet ...

Points, but I'll argue that: (1) Such plummeting would prove that the stock valuations were already very near the peak of a bubble, if not fraudulent. And (2) billionaires making that argument is a perhaps-legal but horribly immoral sort of Stockholm Syndrome move - telling a large number of equity investors "either I get my way, or things will get real painful for you".

> ... thinking about why ultra high net worth individuals refuse to pay taxes ...

I'll argue that most of the ultra-rich got that way through some combination of pathological obsessions with wealth and power. And their social environment skews very heavily toward (1) peers/rivals/friends/family with such obsessions, and (2) underlings/petitioners/fans/admirers with (at best) very unhealthy fixations on wealth and power.

> The idea that their class can be maintained when the base ...

Yep. https://en.wikipedia.org/wiki/French_revolution#Causes

My read of history that many in the ruling classes of other European countries really learned that squeezing their own lower classes too hard could end horribly for them. But human memory, even institutional, fades with time. And "this time is somehow different" is a perennial and seductive belief.