I like the implied reasoning saying that "Other governments are willing to take a bigger slice of the fruits of your labor, so you have no grounds to complain." Except I don't, actually.
Of course, the bigger flaw with Mankiw's argument is that it evades the point of those taxes, which is that they buy things that our society has deemed worth having. It is not totally outside the bounds of reason to suggest that we'd have less entrepreneurship if every potential business owner had to worry about providing for 100% of their parents medical expenses.
We cannot have everything we want. At some point, the goal of having the "Happiest Possible Greg Mankiw" will have to give way to something like Wildland Fire Management.
It is less than honest to suggest that the tax increases we are discussing will be used for things like fire protection. The vast majority of government spending these days is not providing public goods. Police, fire, defense, the CDC and other public goods make up a relatively small portion of the budget.
For the most part, the extra money Mankiw pays will simply be redistributed to people less productive than him (federal bureaucrats, people capable of working but who don't wish to, corporations less productive than competitors/alternatives). If you wish to argue that those are useful purposes, be my guest.
However, the dominant component of "people capable of working but who don't wish to" is --- by my casual analysis (please correct me) --- retirees on social security. It's also dubious to suggest that if we drastically cut back on the social safety net that the entire entrepreneurial class would necessarily fare better; many of us[1] would have to redirect our efforts and risk tolerances to fund our parents retirement.
We probably agree more than we disagree on the subject of civil servant pensions.
I am willing to accept that there is no tax/spend scheme that is ever going to make me entirely comfortable (a single trip to the DMV illustrates this nicely) without rejecting entirely the idea that we should trade off some personal incentives for our collective well being.
[1] Not me, though.
It would not be necessary for young people to fund their parent's retirement, their parents would not necessarily need to retire. A large number of older people are capable of working, and the latest projections suggest that this trend will only increase in the future:
We likely agree on ratcheting up the retirement age.
This argument plays out like a chess endgame. Can we cut to the chase and acknowledge the tradeoff that's being made? At some level, we as a society are trading units of Mankiw happiness for units of peace of mind about retirement.
We certainly do it inefficiently, and, in particular, we drag alone a whole class of free riders who create a drag on the operation of our local and state governments. But even if we optimized all that away, the same fundamental response would apply to Mankiw's argument.
I am not simply pointing out that "taxes buy stuff" --- though that is also a valid point to make. I am saying that Mankiw ignores an offsetting form of incentive to work and (particularly) take risks: the well-being of our close relatives.
Again, it may very well be more than the claimed 90% tax rate. I also realize the professor has a vested interest (for several reasons) in knocking the tax cut expiration. But the United States tax system is complex beyond belief and I think any comparison with other countries is never simple.
Edit: Or higher than the 'real' tax rate if the professor is pushing the numbers in his favor (likely).
The "complexity" of the US tax system is orthogonal to the issue we're discussing.
Without doing the research to prove it
You'll notice that US/NYC is 21 and US/IL (where I'm at) is 35. You should also notice that many of the >35 burdens have a large VAT/Sales Tax which has less impact on the top 1% of earners.
Again, I'm not an expert in these matters. And, in any giving country the professor may be paying more in taxes. However, to systematically dismiss the tax burden of the United States because we have a low income tax isn't taking the full picture into account.
This seems like the appropriate comparison to draw, since it's the metric Mankiw himself evokes.