Even with preferential treatment of LTCG, high earners still pay a disproportionate share of income taxes (which include capital gains taxes).

The real bias in the tax code is, perhaps unsurprisingly, around the median income, where many expenses that the poor do not incur to the same degree (home ownership, college tuition, IRAs) are highly subsidized, with most credits and deductions dropping off as you hit a higher income level.