I'm no expert. However, I think taxation becomes immoral when the amount you pay in taxes, is more than the amount that you keep... so anything above 50%?
Anyway, taxes don't matter. All taxes return to circulation (unless government is radically changing economic policy). What people are really saying is that they want to be better off than some other group of people.
FYI, he paid 14% federal because most of his money came from carried interest which is taxed like dividends. The 14% is only after the same income is taxed at the corporate level at 35%.