it’s such a serious threat to the country’s financial stability that we should chicken out and stop taxing the rich.
No one's saying this, this is a straw man.
It's just a simple fact that there is a 'sweet spot' when it comes to maximizing tax revenue. It's the same as if you're selling a product for $10, then 100 people buy it, and you assume that you'll double your $1000 profit if you sell it for $20 instead, but then the number of buyers went down to 10, and now your bottom line is $800 less, instead.
"Just tax them more" is not the simple/obvious solution it appears to be on the surface. Also, people don't just not react when stuff like this changes, to protect themselves; just compare tax revenue presently to what it was when it capped out at (iirc) 91%.
And even IF 'turning that dial' simply increased tax revenue, it needs to be combined with that revenue being spent productively, for it to make any difference at all. Hell, I think the US already brings in more than enough tax revenue to do everything we want it to do, if it was doing it as efficiently as it could be.