It's very possible to get capital gains on something that has not been already taxed as income.
For example: say you purchased 100 shares of Tesla stock a decade ago and sold it today for lots of capital gains. But Tesla has never posted an annual profit on a tax basis, and thus the "income" underlying the shares you sold was not taxed.
In fact, the capital gains rates were never about avoiding double taxation. It was simply a giveaway to Republican donors by the Reagan administration.
You probably mixed up capital gains and dividends. The logic behind giving dividends special rates (including a 0% rate for certain inter-corporate dividends) is that the corporation paying the dividend has already paid an income tax on those profits, so the shareholders should not be subject to full tax on the shares of the profits they receive, but should still pay some tax to account for the benefits of using the corporate form.
For example: say you purchased 100 shares of Tesla stock a decade ago and sold it today for lots of capital gains. But Tesla has never posted an annual profit on a tax basis, and thus the "income" underlying the shares you sold was not taxed.
In fact, the capital gains rates were never about avoiding double taxation. It was simply a giveaway to Republican donors by the Reagan administration.
You probably mixed up capital gains and dividends. The logic behind giving dividends special rates (including a 0% rate for certain inter-corporate dividends) is that the corporation paying the dividend has already paid an income tax on those profits, so the shareholders should not be subject to full tax on the shares of the profits they receive, but should still pay some tax to account for the benefits of using the corporate form.