(1) Basing ethics on a conception of The Good is inherently tyrannical. Both in the sense of privileging certain people to decide what is The Good and in restricting the lives of those who do not conform that privileged notion of The Good. Hence the importance of "the pursuit of happiness" in the American Declaration of Independence as a principle for a free society, one in which people can pursue their various visions of the good.
I entirely agree with John Rawls that ethics should be concerned with how we get along, not with the pursuit of a singular The Good. We need criteria of judgement because we are purposive beings, but the question “how should we live?” is a different question to “how do we get along?”. (So I also agree with Roger Scruton that answering the second question does not answer the first. From a rather different perspective, Terry Eagleton makes a similar point.)
(2) Such conservatives are apparently committed to an unending war against human sexual diversity. This is a form of utopianism: dealing with human nature not as it is as it is (diverse in erotic orientation) but has it is conceived it ought to be (only one proper sexual orientation). With a history that has all the brutality that utopian wars against human nature involve. (The inherent brutality of utopianism I discuss a bit further here.)
That such anathematisatioin is utopian is obscured by it being “traditional”, though not by the brutality by which the tradition was established and maintained. Its utopianism is also obscured by it being imposed on a comparatively small and vulnerable minority. For there can be few more isolated, more vulnerable or more lonely people anywhere than a same-sex oriented boy or girl reaching puberty in a deeply religious family and community that anathematises same-sex activity and so rejects the legitimacy of their actual nature.
For the largely oblivious majority, such repression could (and can) be passed off as just "normality" or "decency". That some lived in a world of fear, hiding, informers and police brutality, where even to publish a novel which presented homosexuality positively was "obscene"—a quasi-police state in the middle of free societies, whose patterns are familiar to anyone aware of those in the various milder "making the glorious future" totalitarian societies—was a non-happening. It is precisely because modern states have retreated from that required brutality and repression that the tradition of anathematisation and exclusion is collapsing.
That both the opposition to homosexuality and revolutionary socialism are utopian wars against human nature means that there are various affinities between the two: notably the downgrading of consent due to the elevation of form. Just as revolutionary socialism holds workers consenting to work for a firm does not matter because capitalist enterprise is a "false form" of economic action, so the opposition to homosexuality says two men or two women consenting to have sex does not matter because same-sex activity is a "false form" of sexual activity.
There has also certain been a certain "airbrushing" of history, so quite false statements get passed off as "obvious" truths. An example is:
“until this generation, gay marriage had been sanctioned by no society that we know of, anywhere at any time in history”from columnist Charles Krauthammer, which is either smug ignorance of much anthropological data or else arch narrowing of terms. Even supporters of same-sex marriage such as Steven Schmidt can make statements such as:
“The institution of marriage is the foundation of society and alterations to its definitions shouldn't be lightly undertaken. It has always been defined as the legal union of a man and a woman, and it's understandable that many Americans are apprehensive about making a definitional change to so profoundly an important institution.”while standing in a land whose preceding cultures included ones that included same-sex marriages.
(3) Homosexuality is discussed as an "optional extra" rather than manifestation of how (some) people are. But that is profoundly disingenuous. Disapproval of homosexuality is not mere disapproval of certain sex acts (even those—oral sex, anal sex, masturbation, etc—which have their heterosexual equivalents), it is disapproval of love expressed by such sex. Of building lives together bound by erotic love. It is a disapproval of people’s lives in a quite fundamental sense.
To justify such on the grounds of a commitment to a conception of “human flourishing”, as Rod Dreher, Edward Feser, James Kalb and others do, is a conception that clearly excludes a whole set of people from the definition of humans-whose-flourishing-counts. (Any notion that such exclusion is in their “real” interests is just a monstrously disingenuous rationalization.) Indeed, it is a conception of “human flourishing” which entails creating human misery for those who do not conform to its notion of the proper form of the human. See previous comments about the tyrannical nature of ethics based on a conception of The Good.
After all, why be bothered at all that some men love other men, or some women love other women as if such people have to ask permission to live, love and build lives together? It bespeaks of a desperate desire to enforce a particular conception of the human.
The traditional Christian position has been to be as cruel to the same-sex attracted and oriented as can be got away with. If burning them alive can be got away with, that was done. If throwing them to dogs to be eaten alive can be got away with, that was done. If it is to be gaoled or flogged, that was done. Any way the message can be sent that they are contemptible and disgusting, that was done. As philosopher Richard Mohr observed:
unenforced sodomy laws are the chief systematic way that society as a whole tells gays they are scum.If the message can be sent that daring to think themselves the equal of “real people” with “real relationships” is unacceptable can be sent, that is done.
The wonder is, people can believe that the God who sent His only Son to die on the cross for their salvation nevertheless also wants them to be as cruel as they can get away with to a particular vulnerable minority. The trick is to pass it off as not being cruelty, but as defence of “decency”. An old trick, but rarely done with such fervour as against the queers.
(4) The experience of being homosexual (and so the implications of "our disapproval counts because we have the numbers" for homosexuals) has no weight. It is just not a set of experiences or aspirations that count at all. So no cruelty to them in the name of "defending decency" counts as cruelty, which is how the believers reconcile their commitment to the Gospel of Love with inflicting as much cruelty as they can get away with without presenting it (above all to themselves) as cruelty.
So, to sum up (the opposition to homosexuality), homosexuals should not exist, they should not act upon their existence as people erotically oriented towards their own sex, the law should not positively recognise their existence, and should not protect the lives they build together. So, the fight is between the growing view that homosexuals are just folk—in the words of philosopher Kwame Anthony Appiah:
over the last 30 years or so, instead of thinking about the private activity of gay sex, many Americans and Europeans started thinking about the public category of gay people.—versus the view that they are a twisted and perverted lesser form of the human whose experience and aspirations do not count. I know which side I am happy to be on.
ADDENDA: I have edited this post a bit to clarify some points, add or extend others, fix some grammatical errors, etc without changing the basic arguments. It is something of a work in progress.