I appreciate the Christians weighing in on why they oppose gay marriage and trying to explain how they think people are harmed. One genre of response has turned up in thread and is fairly widespread, so I’ll try to address it. Anonymous wrote:
Many people are wondering why infertile heterosexual marriages are considered moral and praise worthy while homosexual “marriages” are not. The reason is that in an infertile heterosexual marriage the sexual organs are, at least, being used for the purpose for which they were created, or if you prefer the purpose for which they evolved. In homosexual sex the sexual organs are abused. Penises were not meant to be rammed in to an anus. Yes, this means oral and anal sodomy are considered immoral even in heterosexual relations. Societies lacking Divine revelation had to formulate moral laws based on what was available to them namely Nature. This is why there are still laws against these kinds of behaviors in some places.
…Animals are not rational creatures so are not expected to follow Natural moral law. Humans should be expected to act according to reason.
When I read this claim, it sounds like Anonymous is conflating two ideas: Natural Law and the Law of Nature. Before I go on, here comes the caveat: I’m not sure precisely how Christians use these terms, so don’t try and use this distinction in other contexts and don’t complain in the combox that I’ve used them incorrectly (but feel free to suggest better or clearer terms).
Natural Law is normative. It’s the moral law we see as binding on humans and tolerably accessible whether through intuitions or reason or what have you. This is the law written on the hearts of man — it is accessible to all (or practically all) people without revelation or belief in a particular god. A Christian wouldn’t hold me to account for missing Mass on a Holy Day of Obligation, since I don’t understand it’s a sin, but they would fault me for committing murder, since I can be assumed to know it is wrong.
The mechanics of sexual organs falls into the Laws of Nature category for me, so they don’t get a privileged spot in my moral calculus. It may be unnecessary for procreation to put some protuberances in certain orifices, but there’s no great evolutionary justification for enthusiastically bringing together the entrances to our alimentary canals and I don’t hear many people railing against kissing for pleasure.
To convince me that gay sex is morally indefensible (whether as part of a committed relationship or not), you’re going to have to bring the discussion back into the Natural Law side of the debate and tell me more about who it hurts and how. Remember, I’ve got major transhumanist and gnostic sympathies, so you have a lot of heavy lifting to do to convince me that thwarting some of the inclinations or actions of the body is wrong.