No, capital gains are "unearned income". Income which magically appears when the investor sits there, does nothing, and watches a successful investment grow. It can't be taxed previously because it never existed previously.

During the HW Bush years taxes on long term capital gains were 28-33%, rates which are similar to the tax on income that wealthy people paid, and still do pay on income they actually WORK for. I guess they thought that was fair in those days. But Bush Jr. supported lowering the rate to 15%, matching the lowest rate in history. Those who say a low rate encourages investment and creates jobs now realize after our experiences with the recession, that lower capital gains rates only increase the national deficit and put extra money in the pockets of the wealthy.