Capital gains are treated differently than normal income because it is the pool of capital that allows the economy to grow. That's why, every time we have dropped the Capital Gains tax over the past half century, it has resulted in increased tax revenues overall. And that's why Sweden, the most "progressive" of the European socialist countries, recently took the "radical" step of dropping their capital gains tax to zero. There are a host of arguments to be made for treating capital gains differently than ordinary income, and Charles Krauthammer makes a lot of them in the video below.
(H/T Nice Deb)
I would just add that Obama's Fairness Doctrine is the pure and unadulterated language of socialism. It is not the language of capitalism.