Alright, so James is misinformed (at least according to Jens) but I'm not exactly sold on pronouncing humanity without hope and moving to the forest yet...
They're tax exempt because they have no representation in government.
You start taxing them and nearly every republican will donate to the ones that push their view, and the millions they disburse to charities would go to politics.
In 2021: donations to Christian organizations was over 23 billion dollars. Anyone else wanna start taxing churches?