Exactly. Free citizens entering into whatever personal and financial and religious arrangements they freely choose.
. . . with the state only granting civil union contracts to couples wishing to enter into an agreement.
Uhhh, no. That's just a semantic change. The government has no business "granting" anybody pre-fab contracts with which to arrange their personal relationships.
Like I said, no on civil unions, yes to Holy Matrimony.
It is done to promote stability in parenting relationships.
Not every marriage ends up with kids and not every marriage sanctioned by the state ends up stable, but, that’s no reason to ditch it.