Here is the proper way to understand the SALT issue—whether State and Local Taxes should be deducted from taxable income on which federal taxes are levied.
Assume that taxpayer 1 (Jack) in state A and taxpayer 2 (Mary) in state B both have earned incomes of $150,000 each. If Uncle Sam needs to raise $60,000 each year from its income tax and applies a flat tax on each taxpayers’ total income, it would need to impose a tax rate of 20% (150,000+150,000=300,000*0.2=60,000). Each taxpayer would pay $30,000 in federal taxes.
Assume that Jack chooses to buy an expensive car costing $100,000 while Mary makes a more frugal choice and buys a $40,000 car. No one would think that they should be allowed to deduct the cost of their cars from their incomes for purposes of their federal income tax, but what if they could? Jack would now have $50,000 in federally taxable income (150,000-100,000) while Mary would have taxable income of$110,000 (100,000-40,000). To raise the same $60,000 needed by the Feds, the federal tax rate would need to be increased to 37.5% (50,000+110,000=160,000*0.375=60,000). Of the $60,000 in federal tax revenue, Jack would pay $18,750 (50,000*0.375) and Mary would pay $41,250 (110*0.375). Not only does Jack get a better car but he also pays less taxes. In fact, this tax treatment subsidizes Jack’s expensive car to the amount of $11,250 (30,000-18,750). This is likely to lead Jack to buy a more expensive car than he would have chosen if spending only his own money. Clearly that would be neither fair nor economically efficient.
Replace “car” in the above example with “state government expenditures”. Jack may well choose to have (and pay the higher taxes to finance) more extensive state government services than does Mary. That is fine as long as you are free to choose whether you live in state A or state B. But should Mary be forced to pay (subsidize) some of Jack’s tastes for larger state government expenditures? Surely not, but that is exactly what allowing tax payers to deduct their SALT from their taxable income for federal tax purposes does. Eliminating that deduction would restore fairness and remove any artificial inducement for larger state expenditures. In this way, every one would be free to support the level of state spending they are willing to pay for.