I was asked recently what Christians, especially in America, seem to spend so much of their time thinking and complaining about homosexuality.
This was my off-the-cuff response;
The acceptance of homosexuality is right now the leading edge of the promotion of an ethics of relativism. If there is an agenda, it is to use homosexuality as a way of promoting this view of morality.
The idea is that all moral judgments are only subjective. Now, almost no one actually believes this, and absolutely no one lives that way, but that is the unspoken creed. It is generally formulated in the negative; "Who are you to judge what I do?".
But while holding to the creed in the abstract, we are in reality very happy to judge one another's actions many times a day. Because no one really believes or lives as if morality were subjective (it would be impossible), public morals under that philosophy work out always to a matter of mere brute politics. Through an elaborate public hypocrisy, fashionable vices are tolerated or promoted, less fashionable ones are frowned on or suppressed. If you can swing enough people into siding with you (through any means at all - social pressure, the threat of legal action, bullying, bribery, persuasion, flattery, etc...) you can gain at least some kind of official approval of your favorite sin.
So you have, among those who would like relativism to replace the more traditional Judeo/Christian moral code, a tacit agreement; "I won't criticize your vice (in public), if you won't criticize mine". So those who would like a little more latitude to cheat on a spouse, or do drugs, or unplug grandma's breathing tube, for instance, without all the bothersome public shaming, are more likely to support anything that advances a more relativistic moral viewpoint, even if they (at first) find it repugnant. Gay rights happens to be the flagship of moral relativism at present, which is why you hear of it so often.
Not only that, but homosexual behavior is so obviously opposed to reason (the natural law) that its acceptance sends a very potent message that the Old Law (traditional morality) is officially over and done with, has been completely overturned.
This is also why (from this point of view) Christians must be at least marginalized and taken out of public discourse; by not honoring the Code of Silence, they're getting in the way . Making things difficult. The very idea of a transcendent, absolute morality that applies to all people in all places threatens the whole relativist worldview. No one likes to feel ashamed, and there are two ways to prevent this kind of moral discomfort; Christendom works to continually conform society to the moral law. The New Enlightenment works to continually conform the moral law to the society.