I'm not an economist or finance person, so I don't know why we really ended up where we are. I think a lot of people in this thread, and most of the non-investment-wealthy people in the US, would say it's because of lobbying and so forth to let the rich get richer. That may be true. But I am open to the idea that research and modeling points to this being good overall even if it appears to be (or: is) unfair to 'average' Americans.

I'd like to see some (comprehensible to a layperson) discussion about what would happen if all income - wages, tips, gifts, inheritance, interest, dividends, capital gains, etc. etc. - was treated dollar for dollar equally from a tax perspective. I don't understand why it couldn't be, or why it shouldn't be.