That's an entirely different debate. But if we are going to have voluntary tax-exempt status, the same rules should apply across the board.
"... if we are going to have voluntary tax-exempt status ..."
Ah, but that's just the point!!! There's no valid reason for retaining such an income tax system as our tax revenues can be raised more efficiently and more cheaply with the FairTax while benefiting almost all taxpayers as well as the economy of the country.
For those of you not familiar with the FairTax, here's the bill (HR25). And it's a very interesting read.
In addition, there's a world on information on FairTax website.
There's lots of helpful information there on many, many different topics. Check the FAQs and Rebuttals for example.