the argument that there will be more gay relationships is absurd.

So you're saying that if the state sponsors an activity and society approves of it, it won't increase?

first of all, people 'end up' in relationships of any kind because of their genetically determined sexual preference and to suggest otherwise is absurd.

There are numerous accounts of people who started life straight, had a traumatic experience, and then started having gay relationships. For what it's worth, this has happened to several people that I know personally and have for years. Of course, examples don't prove rules, but they do disprove rules. (That's basically how empiricism works.)

there is no distinction between someone's natural sexual preference and their sexual preference.

A moment ago you suggested that sexual preference is genetically determined. Let's call that their natural sexual preference. Now, let's look at homosexual relationships in prison. It's clearly not their preferred arrangement-- many of them have wives and families on the outside-- but they do it because it's the only sex they're going to get for quite some time. Are you going to argue that they were secretly gay all along? Or do you think that, yes, circumstances and experiences do have an impact on how one's sexuality manifests?

second of all, even if that was true- who gives a shit? let people do whatever they want. people can marry their trucks for all i care.

Sure. But if lots of people began marrying their trucks, do you think you should encourage that behavior? What would the effects be?

the issue of not passing on their genetic material is irrelevant.

It's a little bit relevant, but it's not the entire thing, you're right. Basing an entire argument off of passing on genetic material wouldn't make sense. That's just where this conversation has drifted for some reason.

if this is part of your reasoning then you must also think that straight people can only marry if they intend to have children, and any married couple incapable of having children must have their marriage annulled.

It's generally assumed that married couples are going to be having sex. Marriage has at least something to do with the public expression of the intention to have a family together, an instances where this is impossible are the exception, not the norm.

I don't think annulment is really an issue here since my ideal situation is that there be no legal basis for marriage anyway.

A decent part of my concern over gay marriage is that it acts as a symbolic, social affirmation of a certain type of relationship that, by nature, cannot result in children, and probably fosters a high time preference. If you buy into the argument put forth by Hoppe, an average high time preference has a deleterious effect on the continuity of civilization.