Active homosexuality was so counter-intuitive, and so clearly condemned in the Bible, that it has taken a massive 40-year propaganda campaign to break down cultural resistance to it. Here's how it happened.
The initial “intellectual opening” to the notion of a so-called “gay marriage” came about, I believe, with the widespread introduction of the birth control pill around 1960. The primary, essential purpose of marriage is procreation: producing of children as the fruit of the sexual oneness of a married couple.
That’s not to deny the unitive/pleasurable function of marriage, but it is the most important purpose. Obviously, this can only occur between a man and a woman.
Thus, in order to prepare a population for the notion that, somehow, two men or two women can “marry”; first it is necessary to break this immemorial and instinctive connection between sexuality/marriage and procreation.
The flip side of that is the related notion of sex merely for fun; for the relinquishing of desires and biological needs only, rather than for the purpose of having children and being open to conception when and if it occurs. Sex could now be utilized for pleasure purposes only, without “consequence”; utterly disconnected from its deepest purpose.
Legal childkilling [aka abortion] came along in the US in 1973: by judicial fiat, precisely like the ruling on same-sex “marriage”. Just as contraception had separated moral married sexuality from children, so abortion literally separated preborn children from life and the womb and from their place in the scheme of things, by depriving them of their very lives. This was the decisive Step Two in separating both marriage and [heterosexual] sexuality from children.
Once that was accomplished, homosexual acts and homosexual “marriage” became far more thinkable, because if sex need not have any intrinsic connection to children, then (by inexorable logical reduction), homosexual sex would be as “natural” and “normal” as heterosexual sex.
Active homosexuality was so counter-intuitive, and so clearly condemned in the Bible, that it took a massive 40-year propaganda campaign to break down cultural resistance to it. Here is where a relentless, ferociously motivated secularism allied with libertarianism took over. The Big Idea of the sexual revolution was “do your own thing” or “do whatever feels good.”
In strictly legal terms, the notion that government could no longer say anything about sexuality or what goes on behind closed doors, came about with Griswold in 1965 (contraception), which was a direct legal precursor or precedent to Roe in 1973 (the so-called “right to privacy”).
Libertarianism, in its purest secular or popular form: a half-sister of liberalism, dictated that it was no one’s business (last of all, the government’s) to interfere with people’s “personal lives.” The related myth is that none of these things affect anyone else. Yet we know from factual statistics that homosexual sex – whatever one thinks of it, morally – has dire health consequences that go far beyond the AIDS virus.
If you want to advocate something, then what you do is simply proclaim (not argue) it, over and over. It’s the old thought of the Big Lie: if you repeat something often enough, people start to believe it, wholly separately from rational argument and fact and previous tradition. This is standard tactics of the Left.
Specifically, how this was done was to appeal to cases where homosexuals had been treated abominably (particularly, sad murders). This is something that any kindhearted person could sympathize with. But admonitions to be kind and loving to all people become mixed-up with accepting immoral acts that the same people were involved in. Today, no one can disagree with what anyone else does without being accused of being “hateful” and “intolerant.” To disagree is to be a bigot and a bad person. That is the fruit of moral relativism.
We've had years of the secularists drumming into everyone’s head the notion that homosexual sex is not a whit different from heterosexual sex (false), and that homosexuals have been treated so badly (true). We failed, too: those of us moral traditionalists who did not act lovingly, and separate the sin from the sinner. The secular world, as always, took that ball and ran with it; milked it for all it was worth.
We also see the “argument” that homosexuality is “genetic” and therefore, cannot be resisted. But there is no compelling scientific evidence for genetic inevitability. The second problem is that the Bible casually assumes that the sin of homosexual sex can be resisted, since it is assumed that it is serious sin, and God doesn’t forbid what is impossible for human beings to avoid. It would be like condemning the drinking of water.
Young people are polling some 80% in favor of same-sex “marriage.” This is why society changed so rapidly. Politicians (and Supreme Court Justices) saw the trend, and started jumping on the bandwagon. Pretty soon it was a fashion, and no one wants to be out of fashion or regarded as a bigot, and all of a sudden a New Norm came about and folks capitulated: not having the spine or principle to disagree and be unpopular.
As recently as 1986 (Bowers v. Hardwick), the Supreme Court upheld anti-sodomy laws. Yet in 2003 (Lawrence v. Texas), this ruling was reversed (as conservative rulings can be, but hardly ever leftist / secularist rulings), and anti-sodomy laws in 14 states were struck down. The so-called “right” to sodomy was now sanctioned, and it took only twelve additional years to create out of whole cloth a supposed right to “same-sex ‘marriage”.
On the flip side, we Catholics have failed to explain why contraception is wrong; how it led to abortion and now same-sex marriage; and we haven't conveyed a vigorous proactive case for abstinence until marriage, the wrongness of sex outside of heterosexual marriage, and the theology of the body. Thus, children were left open to being brainwashed by societal propaganda, with few Christian alternatives being visible or available or even thought of.
This is my own explanation as to why legal same-sex “marriage” occurred when it did. It was a diabolical progression of false, immoral ideas: one leading to the next, and ending up with the legal and cultural situation we find ourselves in today.