Marriage was adopted for the purpose of having children, to simplify. Children need both father and mother to grow up to be well adjusted men and women.
The marriage vows have meaning beyond words. God made woman for man.
That marriage be considered by two homosexuals to each other is unthinkable.
The privilege to marry is not denied to a homosexual man to a heterosexual woman, though I think it would be a very sad situation for the woman.
See “A Libertarian Case Against Same-Sex Marriage,” FreeRepublic.com, Oct. 20, 2008, link: http://www.freerepublic.com/focus/f-chat/2119551/posts