Here are several non-religious reasons against same-sex marriages:
Having read a few of your previous posts, I'm pretty sure you're playing Devil's Advocate here so I'll be sure to respond with the tepidness of someone who understand this.
1. Marriage has always been between a man and a woman.
Maybe in the U.S., but not if you take into account the entirety of human history. Once again, I apologize that I can't quite yet post a link to back myself up here (if you're curious, Google "history of marriage" and look for "History of Marriage in Western Civilization" in the search results - the article you're looking for is at the Magnus Hirschfield Archive for Sexology).
2. Homosexuality isn't "natural."
If by "natural" you mean it doesn't occur in nature, then that's a false assumption. Animals can and do form same-sex partnerships. Though this probably opens a whole other can of worms...
If by "natural" you mean something else... well maybe I should just ask what you mean instead of putting words in your mouth. :sorry1:
3. The purpose of marriage is provide a stable environment for procreation.
I'm assuming by "procreation" you mean purely for the purpose of creating children. Women have the advantage over men (at least for the moment) here in that artificial insemination is available. However, I will concede that before science came along the only way to produce a child was through heterosexual intercourse.
4. Society will fall apart.
This has always been a curious attitude to me. It's an argument that has been used in the past against different things, such as allowing mixed-race couples and such. It's such a telling statement that we always seem to think that X will lead to the downfall of society as we know it.
If society is going to collapse, at least as we (in the western world) know it, it will have nothing to do with allowing same-sex marriages. I don't even see how one might leap that giant logical chasm, especially given that the nations that allow same-sex marriages have yet to devolve into chaos as was predicted by the fear-mongers.
Note that I do not think any of these reasons are legitimate, tho we've all heard all of them.
I know. :sorry1: You played Devil's Advocate, and I decided to respond. I can only hope I didn't say anything insulting.
Then again, I do not think that most religious reasons are legitimate justifications to ban civil marriages either.
I'm a bit of a radical in this aspect, I think. If marriage is supposed to be a religious thing, then it doesn't belong in government period. I feel the same way about many other so-called "religious" issues that the government has decided to tackle. The fact is that we run into a tricky area when marriage is legally recognized, but is also one of those so-called "emotion words" that people get up in arms about. I personally can't think of a good solution that would leave everyone satisfied.
The only religious reason that I can think of that would justify banning same-sex marriages is if you truly believed that your god is so cruel that he would punish all of society for being "tolerant." And if someone truly believes in such an unjust and vengeful god, you have my compassion as your existence must be quite unhappy.
Before I became pseudo-atheist, I wanted to believe that God wouldn't create something and then say "Well, yeah, I created this, but part of it is bad and wasn't really part of my plan." I wanted to believe that God would accept and love his creation in its entirety. But nobody seemed to have the same ideas that I did, and I kinda gave up. Anyway this is kinda off-topic.