I tend to doubt that line of reasoning. People always had ways of avoiding conception and they were rather cheap.
Most of them were either expensive, ineffective, dangerous or a combination of the three.
There has always been cohabitation, premarital sex, adultery, homossexuality, bissexuality, fetishes etc. The real issue is to get people to actually appreciate it or at least not feel strong rejection against it. That is what sexual liberation is about.
Mostly because the spoilt kids copied the values that were previously held by the upper classes of society. Lady Chatterley's Lover, a novel with explicit content, was written in 1928 but was only made available to the public at large in 1960. Before that the book was only released in expensive, rare editions owned by, who else, those with a lot of money.
It's important to notice different types of causal relations here.
Let's use Adam-Eve-Serpent as an analogy. Adam blames Eve. Eve blames the serpent. The serpent, if God had allowed it to speak, could have said that Adam was just copying Eve and that Eve just did what she wanted to, and that if God *really* didn't want them to eat the fruit, He should simply not have made it available in the first place.
Obviously, the serpent is the efficient cause of the formal cause of the whole problem. And because once the formal cause is put in place, all that are within it act without even noticing the limits imposed by the formal cause, the serpent could, in a more complex structure, be "invisible".
Back to our concrete case. The wealthy classes were in the vanguard of depravation *because* they had been listening to these same sources for longer. People like the Frankfurtians or Marx himself to start with, were *always* a product that guilty rich people consumed to compensate for their sense of exclusion for being out of normal society. Contrary to their own claims of siding with "the people" revolutionaries have always lingered around millionaires.
When opportunity came the same "serpent" just pointed to "Eve" who had already been corrupted and, pointing to all their vices used an enchatation that works until today: "look at their *privileges*! You deserve that too!"
Cultural changes always start and are guided by the intellectual elite, although they may become visible only when it becomes pervasive in pop culture. They have the roles either of "angels" or "serpents", shaping the entire phronema within which all facts will be contextualized and acquire meaning. Kings, presidents, tycoons, politicians and generals can be the player moving their pieces to win the game. But it's priests, intellectuals, professors, artists and monks who create the board and the rules of the game.