system
A chat on subreddit /r/NoStupidQuestions
human
Basically any megachurch would qualify as a charity. Many large charities give less than 10% of their donations to the actual causes they champion. There's really no way to require churches to pay taxes without doing away with non-profits as a whole.
gpt
Aside from the political resistance, removing "religious" from the list of exempt purposes would not be difficult or fraught at all. Nor would it have any affect on other NPO's that are exempt for non-religious purposes.