No exceptions should be allowed. If there is a catastrophe or 'strain', then the state tax revenues will go down and the fed revenues also. Having Detroit in Michigan is a perpetual 'strain' on the State of Michigan, or a perpetual catastrophe, as you chose. But stupidity or cupidity should not allow escape from taxes. Government charity turns into entitlements, whether it's by handouts or tax abatement. Keep the taxes low, and let the private sector handle charity.
This proposal also needs to include a firm limit on the amount or the rate that government can confiscate. That was a major flaw in the 16th Amendment. We'd be in a lot better shape now if the income tax had been limited to original 3% top rate.
I do not disagree in principle with the philosophy of your point. I believe in encouraging private sector charity to handle the needs of the suffering.
But realize that the catastrophe/strain exception in the 28th Amendment does not _require_ the Congress to issue deductions, exemptions, or credits in cases such that a State is experiencing catastrophe/strain. - It merely allows Congress the option.
If we remove that clause, Congress still has options - they’re just more expensive. Congress could still pass a bill appropriating funds to pump hundreds of billions in emergency relief to a strained State (a la Louisiana after Katrina). But as we know, anytime the Fed hands out money, it does so with great inefficiency. It’s much better to allow Congress to provide tax exemptions to States that have catastrophes than to ‘triple count’ tax dollars by handing them from citizens to their States to the Federal Government back to a State in crisis. Just in the process of the Fed counting the tax dollars it collects, money gets wasted.
We don’t want to put a cap on how high government can raise taxes because sometimes it is necessary for us to fight wars or deal with financial melt-downs.
The ‘State governments hawking after Federal Government hawking after State governments’ mechanism that the 28th Amendment establishes will keep Federal taxes low by virtue of the competitive and transparent interactions between the two.