You fundamentally miss his point. Even without finding a thousand loopholes to get out of his taxes, he will pay a lower percentage just based on HOW he makes his money.
1) The payroll tax is capped, so a guy making exactly the income it is capped at, and a guy making 100x that, pay exactly the same payroll tax. No accountant required and it is an enormous difference. For Warren, that is millions of dollars right there.
2) Money made from investments is taxed at a lower rate than salary, EVEN IF INVESTING IS YOUR JOB. I personally believe that money you have paid taxes on before should never have capital gains taxes on it - basically you are getting taxed twice. If I choose to take my money and invest it and then buy a car later I pay more tax than a guy who just takes his money and buys a car. So i'm not fan of capital gains taxes. But a guy who gets paid by investing and has no other income should be paying income taxes, not capital gains taxes. How you distinguish the two is definitely hard, but smarter people than me can figure out a way to make that happen.
I would also note that it is worthwhile to be wary of the "double tax" rhetoric. At best, it is an ideological point of dubious worth - i.e., that there is a moral injustice in taxing some money twice. How much moral injustice? Well, I don't know - how much worse is it really than the idea of taxation itself? If I'm okay with being taxed, I'm probably more concerned with how much I'm being taxed, how fair it is compared to other folks, etc., than I am with whether it's two smaller taxes vs. one larger one.
At worst, though, it's a shell game that distracts from what's really going on in the tax code. In everything I've seen, taxes occur on transactions, not on stored wealth. So it's pretty easy to point at any income and outflow and argue that the money itself is being taxed twice. One could argue that the sales tax is a double tax - I'm paying income tax when I earn my paycheck, and then sales tax on the same paycheck when I spend it on groceries.
Anyway - in your example, the non-investor pays taxes on, let's say, $50k of income, then buys a car with it. The investor pays taxes on, let's say, $40k of income, invests it shrewdly, then takes the final $50k out of the investment and buys a car. The non-investor pays income tax on his $50k; the investor pays income tax on $40k, then capital gains on the $10k he made on the market.
The government could have easily taxed the investor on the entire amount withdrawn. That would obviously be pretty dumb, though.
1) The payroll tax is capped, so a guy making exactly the income it is capped at, and a guy making 100x that, pay exactly the same payroll tax. No accountant required and it is an enormous difference. For Warren, that is millions of dollars right there.
2) Money made from investments is taxed at a lower rate than salary, EVEN IF INVESTING IS YOUR JOB. I personally believe that money you have paid taxes on before should never have capital gains taxes on it - basically you are getting taxed twice. If I choose to take my money and invest it and then buy a car later I pay more tax than a guy who just takes his money and buys a car. So i'm not fan of capital gains taxes. But a guy who gets paid by investing and has no other income should be paying income taxes, not capital gains taxes. How you distinguish the two is definitely hard, but smarter people than me can figure out a way to make that happen.