If the income was earned through dividends, maybe this would be a reasonable argument. Most of the time stock just gets bought and sold by investors rather than the company itself though, so it's not clear why corporate tax would have anything to do with this.
Sure, the stock price should somehow be tied to the actual value of the company, but for a while now it's been mostly indistinguishable from a Ponzi scheme other than a few companies that do sometimes decide to buy back some stock, which makes it slightly less sketchy but if the value is from the company buying it back, it's a lot closer to debt or a bond, which is not at all how anyone treats it.
I agree that in a bull market, many corporations are not purchased and sold at book value. That said, we are on the largest bull-run in history, so we shouldn’t treat this as the norm, and base all our long-term decisions on the current situation.
So if I'm understanding correctly, your argument is that it doesn't make sense to make people who make more money pay the same rate of taxes as regular people do because we should ignore the fact that they've been doing it for longer than ever before?
I’m saying that we shouldn’t base our tax policy on a bubble. The dot-com bubble was treated like a solution to the federal deficit, and it wasn’t.