Acknowledging this is a good first step. Now, where do you go from here?

I agree. All public offices should be held by atheists.

Who gets to determine if it's a delusion or a mental illness.

There are many 'choices' of individuals that a political side can call as a delusion/mental illness while another political side staunchly protects.

counterpoint: unless it actively infringes on someone else's rights the entire basis of society should be accommodating people's delusions and mental illnesses.