The Commerce Clause of the US Constitution (Article 1, Section 8, Clause 3) specifies that only the federal government can tax and regulate interstate and international commerce. Without it states would try to pass taxes on businesses in other locations without having to deal with the wrath of local taxpayers. How many states are getting around it is by calling it a use tax rather than a sales tax. This shouldn't pass legal muster since the effect is the same, but as long as the tax rate is the same for local businesses the courts are looking the other way.
Life isn't fair and can't be made so. Is it fair and equal to tax higher income people at special higher tax rates? The definition of fairness depends on whose ox is being gored.
Thanks for providing those points of law. Interesting.