I went for a walk in the miserable heat to get a Dr. Pepper at the gas station, and on the way I got to thinking about something. A lot of people out there say that there's nothing wrong with homosexuality. Their claim is a statement about morality. It expresses a moral point of view. But not everybody who makes the claim makes it from within the same moral theory. As I was walking, I speculated on how people who hold to different moral theories might arrive at the same moral conclusion about homosexuality. They all arrive at the same conclusion, but they get there for different reasons.
First, there are people who believe in objective moral values. They believe certain things are either right or wrong regardless of how an individual or culture feels about it. These people say that although there are things that are objectively wrong, homosexuality isn't one of them.
I don't think it's possible for there to be any objective right or wrong unless there's a God. That's why I avoid secular arguments against homosexuality. For example, the teleological argument against homosexuality doesn't seem to work without assuming there's a God. The teleological argument basically says, "Hey, look at his body. Now look at her body. Obviously they were made for each other. They were not made for the same sex." The whole idea of being "made for" implies that somebody had a purpose in it. If there's no somebody with moral authority who has a purpose in it, then all we can say is that our body parts are more useful in some functions than in others, but we can't say that we truly ought, in the moral sense, to limit them to their more useful function. If a person agrees that God is necessary for morality, yet homosexuality is okay, then they seriously need to deal with the teleological argument against homosexuality.
Not everybody thinks God is necessary for objective moral values, though. Louis Pojman is one example. Since I don't see how it's possible to have objective moral values without a God, I'm not sure what to say to people who take this point of view and say there's nothing wrong with homosexuality. I mean if I assumed their theory for the sake argument, I could say, "Yeah, I don't see anything wrong with homosexuality either. But then again, I don't see anything wrong with anything at all." I suppose a lot of these people, instead of beginning with some foundation for morality in general, will begin instead with some generally agreed upon moral premise, such as If it harms, it's wrong, and if it doesn't harm, it's okay. (I'm not going to go into why I disagree with that premise because it's not relevent to the point I'm making.) Once they find some generally agreed upon moral principle, they could show how the principle, when taken to its logical conclusion, leads to their opinion that there's nothing wrong with homosexuality. You could respond either by taking issue with the premise they began with, or you could respond by showing some mistake in their reasoning from the premise to their conclusion.
Second, there are people who subscribe to cultural relativism. The general concensus of a culture determins what's right and wrong. These people say that morality is relative to each culture, and is valid within that culture, and they say that homosexuality is not wrong within our culture.
I think it would be very hard for a cultural relativist argue for the morality of homosexuality from within their moral theory. It's not possible for the majority of people in a culture to have one moral value while their culture as a whole has an opposing moral value. If there were ten people who made up a culture, and nine of them thought X was wrong, it's not possible for that culture as a whole (or generally) to think X is okay. The only way, then, for a cultural relativist to argue for the morality of homosexuality is to show somehow that the general concensus of our culture feels the same way. They'd have to consult polls or something. I don't think it would be enough to show that 51% are on their side either.
Third, there are individual moral subjectivists. They are like the relativists except that instead of basing morality on cultural consensus, they base it on each individual. Each individual decides for himself whether homosexuality is right or wrong.
There's no point in moral subjectivists making statements to other people about the morality of anything. If they say homosexuality is okay, all that means is that they personally approve of it. But who cares what they personally approve of or disapprove of if it has nothing whatsoever to do with me? Under their theory, I don't gain or lose moral obligations because of somebody else's moral values. There's no point in arguing morality with a subjectivist, because that would be just as silly as arguing over whether or not Cheerios taste good. It's a matter of personal preference. Some people are okay with it, and some aren't.
Fourth, there are nihilists. You could argue that anybody who rejects objective moral values is a nihilists because they are all moral non-realists. They don't believe there are any real moral obligations. There are only useful fictions, or personal feelings.
When a nihilist says there's nothing wrong with homosexuality, it can be taken with a grain of salt. After all, in their theory, there's nothing wrong with anything at all. There's nothing wrong with mother stabbing and father raping. Everything is okay in their theory. Even gay bashing is okay. It's not good, but it's not bad either.
There are other moral theories, of course, but it wasn't that long of a walk, so I didn't get into them.