You've made a misleading assertion;.  Although the income I invest has been taxed, why should I be paying a lower tax rate on the GROWTH of that investment than someone earning employment income by "investing" their labour (whether they are a janitor or lawyer earning employment income)? Add in the fact that many people were gifted the income they have to invest to generate capital gains and dividends, and we have the current status quo driver of wealth inequality: some people who make no real contribution to society benefiting from it at a lower price than others.

I'm a professional earning a decent salary and I supplement that income by investing in stocks and ETFs.  Although I benefit from the favorable tax treatment for passive income, I disagree that should I be taxed less than someone supplementing their (generally lower salary) by working another one or two jobs in the evenings to earn the same amount I "earn" by pressing a few buttons to allocate my excess cash.