Because SS benefits are capped out, and people in the highest tax brackets don't even qualify for Medicare. And capital gains taxes are capped out lower because the investor already paid income tax on the principal. And because investment, not taxation, is what creates jobs in the firstplace (and thereby more taxation).
Incidently, SS and medicare are not taxes.
And what are you doing here on FR?
They're not ? You think they are an investment ?????