The whole point is that rather than the state happily collecting their income tax on any income generated by state residents, which they have always been able to do, they are attempting to levy a tax against all Amazon commerce transactions based on the fact that they have affiliates operating in the state.

DanielBMarkham is not making a case that IL isn't entitled to tax his income from the Amazon affiliate program. It is taken for granted that they will tax the additional income, as they have been doing since before this new budget/law. What they are attempting to do is tax more than just income generated by affiliates living in the state, which is where the argument that they are not contributing to the flow of business which would warrant that.