Taxing capital gains less than ordinary income is a crude method to ensure that you're not being taxed on your losses (in terms of real purchasing power). Unless that's fixed first, there is no way you should be paying for losses.
Based on today's taxation laws, if you bought a stock for $100 10 years ago, and sold it for $110 today, you'll be taxed for the $10 "gain" even though in real terms you lost a fair amount of money. Calculating the real loss (not the nominal gain) is complicated because you need to consider inflation each year into the calculation and the IRS doesn't allow for that.
Not disagreeing that capital and labor need to be taxed at the same rate, but the situation is trickier than just saying "lets tax all gains and wages at the same rate".
Based on today's taxation laws, if you bought a stock for $100 10 years ago, and sold it for $110 today, you'll be taxed for the $10 "gain" even though in real terms you lost a fair amount of money. Calculating the real loss (not the nominal gain) is complicated because you need to consider inflation each year into the calculation and the IRS doesn't allow for that.
Not disagreeing that capital and labor need to be taxed at the same rate, but the situation is trickier than just saying "lets tax all gains and wages at the same rate".