[darklajid]

I'm married. I don't have/follow any religion.

As the sibling stated, this is mostly for law (and therefor state?) related purposes. Taxes. Shared custody. Being able to inquire about my wife's medical situation, should she end up in hospital. Inheritance. Shared property ownership.

Religion is an entirely unrelated, orthogonal (and private, i.e. I agree that the state should have no say here) concept.