> a 100% tax rate wouldn’t pay for the social programs you’re asking for, because the ultra-wealthy just don’t have that much wealth relative to current government revenue levels.

I don't think there are any real proposals to raise taxes only on the ultra wealthy. The super wealthy and the very wealthy would also pay higher taxes (let's say the top .5% of the income/wealth distributions), like they did for most of the post WWII era.

If one is considering raising taxes to create a more equitable society, the upper middle class (say the 99%ile) should also see taxes reset to a marginally higher level, but that appears to be politically less feasible at the moment.