When is consensual sexual behavior between two people ever immoral?
Here are a few thoughts as to why someone might think this.
1. Nature intended that sexual intercourse only take place between a man and a woman, and then only for reproduction.
Response: First, I don't know what "nature" is, and if "nature" even exists at all, I don't think it is capable of intending anything. This is similar to a religious or "intelligent design" argument, and there's a crucial question that needs to be asked. "If nature, or God, or whatever intended for us to live a certain way, why is sex so pleasureable, and why is our knowledge of this ideal life so elusive?" If our designer, or nature, intended that our sexual behavior be governed by point 1., they did a rather poor job of it.
In short, the creator designed us in such a way that immoral sexual behavior is rewarded, and we are designed with no innate way of telling which kinds of sex we ought to be having.
Now, how would I argue the immorality of homosexuality without an argument from religion or nature?
I don't see any need to restrict sex to increase the population, so it would be silly to say people can't have sex unless they want to have babies. Recreational sex ought to be allowed, as it increases happiness, interpersonal connections (between couples), and these gains in personal satisfaction translate to a more harmonious society. But this looks like an argument FOR permitting homosexuality.
So, can I make a secular argument against homosexuality? I can't think of anything now, so if someone else would like to attempt, I will help.
