Before we examine gay marriage from sociological views, I think it is most important to examine it from a Biblical view.
Of course, there are the basic rules, laws, and admonitions against homosexual sex in the Old Testament and the New Testament. This should be the first clue that gay marriage may be improper, but it is not definitive. Certainly Biblical admonitions against certain things may be cultural or contextual, so it is always important to discern the operating principle to determine if the rule applies generally.
First of all, Biblically, sex should occur inside the confines of marriage. I hope I don't have to convince you of that, and am going to assume that I don't have to. So then you have the question, can homosexual couples get married? To determine the answer to that one, we need to ask the question, "what is the purpose of marriage"?
Many people say that the Biblical purpose of marriage is children. That is simply not true. The Bible certainly places a high importance on children (Psalm 127:3-5), but it does not list it as the reason for marriage. In fact, the Bible is explicit about why marriage occurs.
Genesis 2:24 says, "Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh." Therefore? Whenever you see a therefore in the Bible, you should take a look and see what it is there for.
The story is about the creation of woman. Why was woman created?
"Then the LORD God said, It is not good that the man should be alone; I will make him a helper fit for him." (Genesis 2:18)
Here's the deal - man is incomplete without woman. The purpose of marriage is the completion of God's creation. That is why, Biblically, gay marriage isn't appropriate - it doesn't complete humanity, but instead represents and incomplete picture of God's creation.
Now, this doesn't necessarily mean that you can only be complete inside of marriage. The Bible also gives another form of completeness in humanity - that of being completed by God Himself. Therefore, single-ness can be appropriate, but only if it God's completion of you is treated as seriously as a marriage.
So, for Christians, it should be clear why gay marriage isn't appropriate. In future posts we will talk about the social case against gay marriage in a plural society (i.e. a society which is not exclusively Christian).