The only difference being that the 'terms of the contract' were put into place by law with a single act.

I have no issue with the 'state' action being 'if any two people want to enter into the the predefined 'living contract, step right up and sign up' as a 'preplan deal'. Open that 'preset deal' to anyone who wants to sign up for it.

And have the separate act of a religious marriage be just that -- a separate act of religious marriage.

I seem to recall going to several weddings in Italy where there was both a 'religious' union *and* the separate 'civil ceremony' that created that relationship with corresponding legal rights attaching.