This argument doesn't make sense at all. Rich people always have access to financial professionals. Shifting tax burdens isn't free and nobody's expecting that

This argument doesn't make sense at all. Rich people always have access to financial professionals. Shifting tax burdens isn't free and nobody's expecting that people won't change their portfolios/tax declarations/whatever to reflect this. What it does do is alter the effective tax rate, and even a partial effect is desirable.