The predominant modes of moral reasoning used by those who declare homosexuality a sin are both deontological: divine command ethics, and natural law. Deontology has numerous limitations, which I've yammered on about already, but among these limitations is that it focuses solely on actions. There is no room for consideration of intentions, circumstances and consequences, let alone more complicated moral concepts like identity and virtue. But these things are crucial to moral judgment.
For example, there is a moral difference between a qualified surgeon who takes a knife and cuts someone in order to remove a tumor, but ends up killing the patient, and the exact same surgeon using the same knife with murderous intent. Or what if an unqualified person picks up the knife with the same noble intent as the surgeon to remove a tumor? Or what if the consequence of the action does not result in the patient's death, but only severe injury? What about secondary moral actors in this scenario like nurses? Does a nurse become accomplice to murder by handing an unqualified surgeon a scalpel?
The branch of moral reasoning that grapples with the ends of our behavior is called teleology, or consequentialism. It certainly can be distorted and abused as any ethical approach can. You are probably familiar with the phrase "the ends do not justify the means." It is true that when taken to extremes certain forms of teleology are repugnant. It is a crass and flawed form of utilitarianism, for example, that is usually employed to justify torture. On the other hand, a person would be criminally insane who never considered the consequences of their actions.
Teleology is biblically supportable. The New Testament, especially, emphasizes the principle of "fruits" - meaning consequences. The phrase "by their fruits you shall know them" is a teleological principal. Indeed, the New Testament is highly critical of deontological ethics. Jesus in his sermons, actions and parables routinely criticizes the scribes and pharisees for following the letter of the law, but failing to be good people based on the consequences of their actions, or their self-aggrandizing intent. The parable of the Good Samaritan is a sharp indictment of deontological ethics, when the Priest and the Levite follow all the rules, but fail to be compassionate.
When we look at the morality of homosexuality through a teleological lens we realize first of all that we can't make sweeping statements. The difference in circumstances and intent between male temple prostitution, pedophilia, prison rape, and a consensual adult monogamous homosexual relationship are vast, as are the consequences. These things are not morally equivalent at all. Furthermore, human relationships are complex and it is difficult to generalize about a group or type of relationships even when they bear substantial superficial similarities. Not all heterosexual consensual adult monogamous marriages are morally equivalent. Why would we assume we could generalize about homosexual relationships?
Unfortunately, these generalizations do get made. Some conservatives have realized that their deontological arguments hold no water and have attempted to wade into the teleological realm alleging all sorts of harm that homosexuality causes. In the next post I will briefly address the question "what harm does homosexuality cause"?