On another thread we are discussing a Pro Marriage Amendment. One of the key functions of this amendment is to bring the expectations of marriage out of case and common law and clearly enumberate them.
In the case law marriage is stated by SCOTUS to be for healthy procreation and stable relationships. This is a scope of behavior the state is willing to support with a license, while most behaviors within that scope are optional.
That some people choose to marry and not have children does not change the total scope of activities the state endorces for all. If you choose not to have children, the state chooses not to offer you certin benifits, such as a Child Tax Credit.
The scope of the license is a buffet of options. Only a couple things are required.