I have a question though. Article I, Section 8 of the Constitution says "uniform throughout the United States", and the Preamble's statement of overall limiting scope says "promote the general welfare" -- which precludes (in theory) any laws or regulation that do not apply uniformly, that is do not favor a class or subgroup of folks over another.
Isn't a "progressive" income tax short of that mark? It hits the class of rich people with a more onerous rate -- a multiple measure system.
And in the states they often have enterprise zones where the sales tax is less or none -- would such tax rate zoning also run afoul of those two Constitutional restraints?
Isn't a "progressive" income tax short of that mark [uniform ]?
Yes, it does. But, an amendment is considered to supersede any conflicting statements that precede it in either the original document or in prior amendments. That's why the 17th Amendment, relating to the election of Senators, is considered to have superseded Article 1, Section 3, of the Constitution (in the news this week).
The 16th Amendment is considered to have superseded part of Article 1, Section 9, of the Constitution, in particular, the phrase:
"No Capitation, or other direct, Tax shall be laid, unless in Proportion to the Census or enumeration herein before directed to be taken."
To read the Constitution and Amendments and see what each Amendment changed, see the Constitutional Issues section of the Action America web site. Start with the Constitution. Wherever you see a link in the text of the Constitution or any Amendment, the linked text is superseded by the Amendment that the link points to.
I hope that this helps.