I have been reading posts by the pro gay marriage side with a lot of mirth. This is the biggest load of tripe amongst them all. Without the union of male and female, there would be no civilization. Period.
The reason we cling so hard to heterosexual marriage is because virtually all civilizations begin to decay when they become sexual free for alls. They do not become more enlightened when morality becomes relative. We can see it in the decay of our own society.