The equal protection clause was never intended to apply to taxes. Even the Tax Protester FAQ (
Tax Protester FAQ) doesn't need to demolish these arguments because nobody ever seems to try to make an equal protection case.
The Minnesota House research department (
http://www.house.leg.state.mn.us/hrd/pubs/ss/clsstxep.htm) has this to say:
Most tax laws are subject to “rational basis” review under the Equal Protection Clause; to be constitutional they must simply have a rational relationship to a legitimate legislative purpose.
The Equal Protection Clause was initially adopted primarily to limit or prohibit racial discrimination by the states. The courts have also applied it to proscribe other forms of invidious discrimination (e.g., based on religion, ethnicity, etc.). However, legislation often necessarily involves “discrimination” in the broader sense that groups of individuals or businesses are treated differently based on particular characteristics (e.g., amounts of income, type of business, uses of property, etc.) that in the abstract are unobjectionable. The clause was not intended to restrict legislation that imposed different tax or regulatory rules, for example, on retailers than on manufacturers. Thus, the U.S. Supreme Court has developed a stricter standard of review for laws that create “suspect classifications” or deprive someone of a “fundamental right” as a compared with more benign legislative classifications. The lines between the two categories (perhaps inevitably) blur at the edges. At times the Court has explicitly talked about a middle level of review.
Very few tax statutes have been struck down under the Equal Protection Clause. The U.S. Supreme Court has generally given states wide latitude to fashion tax classifications, perhaps more than in any other area of law. See San Antonio Independent School District v. Rodriquez, 411 U.S. 1, 41 (1973), where the Court noted: “[T]hat in taxation, even more than in other fields, legislatures possess the greatest freedom in classification.”
You also need to remember that the income tax amendment was passed at the height of the Progressive movement, which called for a progressive tax system (a coincidence using two different meanings of the word). Legislative intent again comes into play. If there had been any thought that unequal tax rates on income would have violated any constitutional principles the amendment could have specifically said so. It didn't then, and not even tax cranks have tried to make the case in the near 100 years since.
In addition, the line of argument of LaMid is based on a false premise, in that the higher tax rate
is not on rich people, as asserted,
but on higher income. Said higher income is potentially attainable by any person, and the tax is not on the person per se but on the income itself.
The argument is a non-starter.