I am starting to be sorry that I asked the question.
However as of this post there has not been a concrete reason given for the need to defend marriage.
Naturally we have inferred that the issue is about sex be it a man with a man or a woman with a woman. It is my experience that marriage is really more about partnership. There is the old joke about the first year of marriage where you stick a bean in a jar for every time you have sex during the first year and after that remove a bean and the expectation is that you most likely will not empty the jar. While this may be extreme, most anyone who is married will agree that after a while sex is not the driving force for the relationship.
So really what is this defensive stuff all about?

Here is an additional comment, which I pose only because I don’t like the descriptor “marriage” for Homosexual unions. What are the components of a homosexual marriage to be formally called…. Husbands? Wives? Spousal Units?

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Sex is a tricky thing best left to professionals.