It's not the only reason... It's not the main reason for some... But it is the Defining Reason... The Marriage of the Flesh existed before we Defined it with our Words.
Only Man/Woman can Possibly EVER Reflect that.
What you are doing is Expanding the Meaning of Marriage, but only Exclusively.
In that you are Defying the Spirit of the Constitution.
You can't Deny (2) Sisters Marriage while Expanding it to (2) Men who aren't Physically Related using ALL of your Arguments Honestly.
Marriage is, has been, and always will be Man and Wife not matter what Society does... Period.
peace...