Just an elaborative springboard off of your posting...
If debating the issue politically regarding legislation, THEN procreation MUST be in there. Those that wish to remove procreation from the debate are those that wish to reframe the issue and debate it illegitimately premised.
What is at issue here is what society wishes to accommodate and merit privileged. The rational basis underlying legislative bodies enacting laws to encourage, support, accommodate, and privilege marriage is PROCREATION. It is not love. Government can not legislate love (divorce laws prove this) and as such can not legislate anything premised in love...
Marriage has not been rewarded by society to promote love or promote monogamous sexual endeavors (both of which are private and as such NOT subject to legislative intrusion or verification). Marriage has always been rewarded by society to promote the BEST procreative environment -one proved historically, one observed by tradition, conventional wisdom, common law, and enacted law...
Precisely.
The male/female union is the only known procreative unit.
The state has an interest in it.
It has no interest in whether 2 people of any sexual combination "love" one another.