1. Historic low labor share
"The labor share of income in the U.S. is currently at its lowest‑ever level in the post‑war period." – saghm
2. Ultra‑rich tax avoidance tactics
"Trust stacking is a recent fad as well, although I don’t have enough data to say whether it is a material concern from a tax revenue perspective." – Silicon Valley Is Obsessed with ‘Trust Stacking,’ and the IRS Doesn't Like It
3. Billionaire power viewed as unsustainable
"The billionaires are literally mentally ill... they will burn this country to the ground before they permit that to happen." – nairboon
4. Capital gains vs. income tax preference
"Capital gains tax is clearly lower than income tax." – ck_one