I think it's the other way around. The question should be why state taxes should take priority over federal taxes. And my answer is they shouldn't. If you can

I think it's the other way around. The question should be why state taxes should take priority over federal taxes. And my answer is they shouldn't. If you can deduct state taxes from federal income taxes, then any increase in state tax rates will take some revenue away from the federal government. If your income is X, why not just have the federal government take Y% and the state take Z%, and have those numbers be independent, so that the total tax you pay is (Y+Z)%? If you want to have higher state taxes to provide more services to residents of the state, that's perfectly reasonable, but why should it be the federal government's role to soften the blow of a state-level policy decision?