"Marriage isn't for each generation to define" --no, it really shouldn't have to be. Yet, what marriage constitutes, and what it MEANS changes by culture and over time.
Marriage used to mean who a woman belonged to. An economic contract between Dad and Hubby, involving an exchange of goods that included the girl (usually too young). Marriage was about getting an extra worker (the wife) to join your family, and it was about continuing the family line.
Marriage didn't used to mean "one man and one woman" -- it meant 1 man, and as many wives as he could afford. This one is especially funny considering that the people who use religion to justify opposition to gay marriage often don't know their faith well enough to tell you which Great Biblical Figures had multiple wives. (Hint: Abraham, Jacob, David, Solomon). Didn't David get in trouble for this? Y-no. He got in trouble for sending a man to the front lines of a conflict so he would die and David could marry the wife.
Marriage didn't used to mean love. That's actually a fairly recent idea. Marriage might've been about who was the right age (and sex) (oh, and not related) in your area, if your community was small. Marriage might've been for status. Oh, and in many parts of the world, people of marriagable age are not considered wise enough to choose for themselves.
Marriage was sometimes forbidden, via class. Feudal peasants often did not marry, because they did not have any land/titles/possessions-of-value to pass on. Marriage served as a means of determining paternity among those who had something to pass on, rather than a matter of stable households, or celebrating love. During America's slave days, no form of marriage was recognized for Blacks.
...so, you want "traditional values"? Great. Women, go make babies. That's all your good for, and clearly we don't have enough starving children and unemployed people in the world. Oh, and men... if you're rich, buy up the women. If you're poor, you'll be dating your hand until someone sends you off to die as cannon-fodder in the next war. (Before you do, you might have a chance to "bond" with some of your fellow soldiers!)
Marriage HAS changed radically. In light of these new changes (monogamy, love, all classes) it is critical that conceptions keep up.
It is not the government's place to tell me who, among sane consenting adults, I may marry. Both examples of what happens when the government gets too involved are about "race," not sexual orientation, but there is much to learn from them.
*America's fears of "Miscegenation" forbade inter-racial marriage in many parts of the country. They said that if we allowed black and white people to marry each other: the white race would die, we'd have to let people marry animals, we'd have to let adults marry children, we'd have to let groups marry, every manner of moral decay would follow. Well, those laws are gone. There are still plenty of pale people. Dogs still can't enter contracts, such as marriage. Age-of-consent laws are still as variable as ever across the country (and globe). Groups still can't marry (not that my white-water rafting team wanted to anyway...). and we have the same frenzied, alarmist attacks against "immorality" wherever we can find it. And we do look hard.
These same arguments are being used against gay marriage. Gee, folks, can't you get more creative? I'm kinda tired of "the sky is falling".
*Nazi Germany. For the purposes of "racial hygiene" marriages between Jews and non-Jews became a matter of legal policy. The government took it upon itself to dissolve some marriages, to priviledge others by pretending that the wife had never been Jewish, and punishing others by labelling both spouses Jews, and putting them both under the tightening regulations of that day. Oh, and this was 1939, before the really bad stuff started. By regulating marriage, we regulate PEOPLE. The further we give our governments the right to pry into our lives, the more freedoms we have given up. If, as opponents of gay marriage claim, marriage is about babies, then nothing stops the government from barring the old or the sterile from solemnizing their unions.
Do you want the government making sure you're "really" a woman before you can get married? How would you feel if the JP wanted a sperm sample to make sure you can actually give your bride-to-be babies?
And finally, on religion:
Religious marriage has usually varied from civil marriage in all but theocracies. If I'm a Catholic, and I get divorced, the Church says I'm still married. If I try to get married, the Church says I'm still married to #1. But we don't have massive protests of Catholics Against Divorce! Traditional Mormons today grapple with marital bonds not recognized by their governments, maybe even actively hunted as bigamy. And that is a shame. But as long as civil and religious marriages are seperate matters in society, religions should not have to feel intimidated when the government has a different idea of what marriage is than they do. Nobody is MAKING Southern Bapitist ministers marry Adam & Steve.
Do I support Same-Sex Marriage? Gay Marriage? Well... actually, no. I support marriage where the government doesn't need to know the sex of me, or my partner. Because it's none of their darn business. As they said in Hawaii... if you'll let a man marry a woman, but you won't let a woman marry a woman, you're discriminating on the basis of sex. Let's take "bride:" and "groom:" off all the forms. Let's switch it to "Spouse 1:" and "Spouse 2:".
Thanks for reading. I encourage dissent.