No millionaire EVER said, "I don't think I"ll bother to make another million dollars, because my taxes are too high." Not. One. Ever.
No corporate CEO EVER said, "I don't think I"ll bother to reinvest in my company, because corporate taxes are too high." Not. One. Ever.
No rich family EVER said, "I don't think I'll bother to amass a bunch of money to pass on to my kids because inheritance taxes are too high." Not. One. Ever.
No investor EVER said, "I don't think I'll bother to invest in new businesses because capital gains taxes are too high." Not. One. Ever.
If you simply lower the tax rates, morbidly rich people just pocket the money and use it to increase wealth disparity between the rich and the poor.