I think what's being referred to was the ability to write off state taxes, which lowered your overall net income in the government's eyes, and thus what you wer

I think what's being referred to was the ability to write off state taxes, which lowered your overall net income in the government's eyes, and thus what you were responsible for paying. It's not that states shouldn't be able to tax, it's that this particular write-off made higher state taxes more palatable at the expense of Federal taxes.