Marriage is a cross cultural constraint on evolutionary mating behavior.You are absolutely right! This argument has baffled me. Why do straight people care? What is the difference between this and saying, for example, if you have brown eyes, you can't be legally married? They always through in the bible too. The bible talks about slaves, we don't have slavery anymore. I have not heard one logical argument for why this group of people should be denied this right.
Gay couples are a defective failure of the very basic purpose and goal of evolution.
Marriage has been present in every single culture in human history, from start to finish. Gay couples have never been accepted in any culture from start to finish. Nor have they established themselves and spread as an acceptable relationship. This is apart from any single religion or belief system.
It is simply idiotic to equate the diverse union of male and female with the redumbant partnership of duplicate genders. The relationship of a male and female are rooted in the very foundation of life, restoration of a single genderless life form.
The differences between marriage with/without kids and gay couples;
An apple tree bearing fruit.
An apple tree not bearing fruit for some reason.
An walnut tree who never bears any fruit wanting to be a apple tree.
An walnut tree hanging apples on it's branches pretending to be a apple tree.
The claim that if the government doesn't 'require' apple trees to bear fruit, then it is discrimination not to call walnut trees apple trees too!
Do you want more? Perhaps the distinction of natural sex vs Pete and RePete?