With a deduction for state tax, it's a lot more cut and dried "hey I don't have this money anymore because the state whose laws you officially sanction by virtue of their being part of your union is going to throw me in jail if I don't pay them".
I'm not sure if that's more or less cut and dried than "hey I don't have this money anymore because I had to pay money to not be literally homeless".
Deductions are an approach to reducing tax burden, but ultimately we have to decide if more taxes or less taxes are the way to operate our societies. The federalized tax system allows different states to experiment with different approaches, and these kinds of deductions incentivize behavior in one direction.
Should someone living in a luxury penthouse suite at 15K+ a month get to deduct his rent at 100%, as well as closet-sized studio apartment? If not, where is the line drawn?
This is what I mean when I talk about value-based judgements based on variable rates.
Should I be able to deduct only what is literally the cheapest rent in my city? What if the cheapest apartment is full, and there's no way I could possibly get that rate? Should it be the cheapest AVAILABLE rate? Would this then impact prices knowing that the lowest rate drives tax-deductibility for all citizens?
This is the labyrinthine decision tree that opens up when deducting things like rent, food, clothing, etc.
Also, if SALT deductions truly incentivized punitive state taxes, why are so many states still charging 0% tax rates?