Believe it or not... we have among the highest corporate tax rates in the developed world.
Of course corporations get to write off almost all costs and not pay taxes on their gross income, but only on the profit... which is why they get a tax break for giving their employees health insurance, which the employees themselves wouldn't get if they bought it for themselves.
Taxing churches won't get what you want though, what would end up happening would be the funneling of money to tax havens and people would suffer not churches.
At least they would learn they no longer enjoy their privileged status.
Some churches engage in business, perhaps by owning properties they rent. Some of these churches have evaded taxes by not reporting their business income. Some decades ago, a Dayton, Ohio, church was found delinquent and had to pay.
The question here is, Should atheists push for taxing all church property?
I fear politicians will find justice less important than the protests by churchgoers.
Because winning experiences are better for morale than losing experiences; let's choose efforts we can win.