j.d. foster is with the conservative heritage foundation. >> a capital gain is a tax on a change in wealth. it's really a wealth tax, it's not an income tax. we integrate the two systems because it's convenient to do so, but a capital gain is a change in wealth, it's not income. >> reporter: he says in many cases, capital gains are already taxed at the corporate level before they ever end up on an individual's tax return. the lower rates also encourage investment, helping grow the economy. but critics don't buy it. >> we have a long history of different capital gains rates over almost a hundred years, and there is no evidence that it helps the economy or even helps investment. >> reporter: bob mcintyre of citizens for tax justice says the tax code's treatment of capital gains creates confusion, complexity, and plenty of ways for people to score lower tax rates. >> it's also the reason why... the biggest reason why the tax code is so complicated. because people who can do it take their wages or ot