There is no "correct" way to collect tax. Taxes are collected to 1) pay for government expenditures, and 2) influence behavior.
Well, #1 is close to a trillion short, so out goes that reason. But still, governments need a way to collect revenue, while making some attempt to make it "fair".
As for #2, it has now become political to the point where influencing behavior is gone. Taxes are set by those in power to favor those that helped them gain that power.
Capital gains tax has been less than ordinary income tax for decades.
It's purpose is too encourage long term capital investment in assets that carry a greater risk than investments that produce ordinary income (CD's, Bonds, etc). Businesses trying to raise capital would have to pay more for investments that will be taxed at ordinary income rates. The Federal government decided a long time ago that it was a good idea to encourage investors to buy stock or real estate, so they reduced the taxes on the appreciation in those assets.
Dinking around with tax rates is no good. Savers/investors need some degree of confidence that they understand the tax cost on the other end. Stability is the answer, not frequent tinkering.
I had a very sweet elderly widow as a client. Her income was almost all dividends. When the dividend rate was cut in half, she saved over $20k in tax. Knowing that she was not exactly in need of government assistance, she asked me, "Why did they decide it was a good idea to cut my taxes?". I explained to her that the government hoped she spend the savings to help stimulate the economy. She replied, "Well, I guess I do need a new washing machine." So much for changing her behavior.