What is marriage after all? Check out the dictionary and it summarizes it by the saying of vows between a man and woman. Or it can be a nautical term when you marry two ropes together. My Etymology Dictionary tells me that it comes from the Middle Ages. Marry is a Latin term (mari) which stands for "a young women." The thought was that a priest would provide a mari to a young man and so he would be "married."
By definition only young men and young women could be married. But our definitions change all the time. In fact the new dictionaries will have a reference to same-sex marriage. So where do we go with this whole marriage thing? Should whoever and/or whatever be allowed to get married? Let me give you a few facts as I have read them in the last year.
Fact #1. Gays and Lesbians want to get into a committed relationship and want to have the legitimization of society on that union.
Fact #2. Gay and Lesbian couples ALREADY HAVE the same rights as married couples; all they have to do is sign a few legal documents. (Guardianship, beneficiary, etc.) So the argument is for something more than simply the same rights.
Fact #3. The United States would not allow mixed race couples to marry less than a hundred years ago. Now it is normal. But this is different then same sex marriage IF you consider sexual orientation a choice. If you don't consider it a choice then you can draw the analogy. However; most current studies and logic will tell you it is a choice.
Fact #4. Sweden allowed same sex marriage in the 80's. Since then marriage has virtually been eliminated as an institution. Less than 20% of the people still get married, most don't see the point. Most simply live together and 90% of the kids are born without the benefit of marriage.
The conclusions that I draw is this: There is something special about a marriage between a man and a women, special for the couple, special for the kids, and special for society. If we lose this institution we all will lose: men, women, kids, and society. I believe allowing anything other than a man and a woman to marry will kill the institution and I believe that institution is worth fighting.