Because as I explained earlier, that makes sense. It doesn't preference the wealthy exclusively like many other types of deductions because middle income people also invest in property and securities. In fact, the best way up in the world is buying a duplex instead of your dream home. So, you live in a less desirable neighborhood in smaller digs but someone else is paying the mortgage and as soon as you have enough for another downpayment, you buy another one. Long term capital gains are taxed at a lower rate because you are mostly taxing inflation which in itself is also a tax. Short term gains (< 1 year holding period) are taxed at ordinary income levels.
So, yes, the more of your income that is capital gains, the lower your effective tax rate. What you do see through from the first chart is that the lighter blue tier is disadvantaged by the current system. They are the group that could be paying less. They are the upper middle class. The well off but not wealthy people.
Other graphics. The numbers may vary slightly depending on the year the graphic was created.
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