> When you “tax the rich at 90%” it disincentivizes people from working
It reduces the incentive to sacrifice other things for additional income once you've already reached the level at which the increased tax kicks in, yes.
So what is a “fair” amount that people should earn? I bet the people living in the Midwest would love to tax the “liberal west coast elite” living in Silicon Valley 90%. Should 90% start at $150K? $200K? Or is the definition of the “rich” “anyone who makes more than I think I will make”.
> So what is a “fair” amount that people should earn?
I reject both the concept and it's relevance; no marginal tax rate below 100% is an income ceiling, and setting marginal tax rates at particular levels neither requires nor implies that a single such “fair” amount exists.
> I bet the people living in the Midwest would love to tax the “liberal west coast elite” living in Silicon Valley 90%
I bet most of the low income population of the West Coast (and Bay Area in particular) would like that—and benefit from it, in terms of effects on local cost of living—more than anyone in the Midwest.
> Should 90% start at $150K? $200K?
I didn't actually endorse a 90% marginal rate for federal income tax; disagreeing with a particular argument against a thing isn't endorsing it.
If I were to propose rewriting marginal rates, I'd probably do something like drop the 32% bracket down to start at about the 90th individual income percentile (instead of about the 95th, where it is currently), and drop the existing higher brackets in favor of adding additional +8% brackets at the 95th, 97th, 98th, and 99th percentiles, topping out at a 64% rate.
But more important, I'd tax capital gains as normal income, with options for both advance recognition and deferment to handle irregular streams (whether from capital events or otherwise.)
It reduces the incentive to sacrifice other things for additional income once you've already reached the level at which the increased tax kicks in, yes.
Why is this a bad thing?