...why can't I get tax-exempt status?

That is a mistake that religious apologists often make, because they think that they can prove that atheism is a belief, which is quite correct, it can be, ( Not always but sometimes.) but the mistake is in thinking that a belief is the same things as religion. But it is not.

A belief is something we hold as probably true without supporting evidence, where a religion is something we hold true without evidence but support with fake authority. As in. "Because my holy book says so." "Because my tradition says so. " " Because my God says so. " Etc.

Religion in short is the same thing as the fallacy of proof by authority. And is quite different from honest belief, which accepts that it is belief.

Atheism is not a religion, but good point that while many atheists disagree between themselves about many other things besides religious beliefs, they generally agree to disagree and often try to use reason and logic rather than violence to persuade others to their point of view, as evidenced on this site. We might see a "war of words" sometimes, but generally atheists find peaceful ways to deal with disagreements.