Well, no one knows what the ideal point to maximize government revenue, the high point of the Laffer Curve, would be. The economy is too complex. But logically, it’s probably somewhere around 50% total, thus probably a bit more than 50% for marginal rates. In fact, since the rich don’t invest every last dollar in such a fashion as to increase the money supply; & since an increased money supply means inflation & a loss of purchasing power per dollar; it may be more effective to increase marginal rates past 60%. We just don’t know. But under 40% is probably too low, unless state & local taxes are taking a bite of over 10%. Considering some states don’t even have income tax, I support top marginal tax rates over 50%.
The opposition to taxes in this range is mostly moral: There’s something icky about potentially demanding a majority of a person’s compensation. But I prefer high taxes to high public debt (& thus even higher taxes long-term), myself.