The advent of birth control itself can't be the main cause. I think the biggest problem is that the social stigma associated with having children out of wedlock eroded over time. It used to be that women who did that were social pariahs, but not anymore. Now they don't get married just so they can rake in the welfare benefits.
No-fault divorces also surely helped in that marriage can so easily be dissolved, fostering the attitude that marriage isn't sacred anymore. And all the children bearing the burden of that grow up in single-parent homes, and I believe just about every study done on the subject shows that such homes are not as good as two-parent homes for raising moral, well-adjusted kids (the kind who are less likely to sleep around a lot).
Looking back on that text, it seems to be a vicious feedback loop.
You will not be surprised to learn that I think that it was the onset of The Pill in 1961 that produced the conditions that broke down the social stigma of having children out of wedlock, and created the social conditions that led to rapid adoption of no-fault divorce.
I probably ought to explain myself (and probably wouldn't be able to restrain myself from doing so even if I oughtn't).
What female contraception - The Pill - hit dead center on was the basic human desire to have unfettered, spontaneous and unprotected sex. Without being too crude, before The Pill, there were only condoms. The social stigma was there, so females (who are the ones who need the protection) certainly would not go in and buy them. And males? Males have never been very responsible about that sort of thing. Besides, condoms are not spontaneous...you have to actually HAVE one at the time...and people would PREFER to engage in sex without them, because it feels better.
Sorry, but that's the case.
The Pill eliminated that immediately. A woman got it from her doctor/pharmacist, so all of the stigma was gone. She controlled it herself - the male was completely uninvolved. And THEREFORE sexual spontaneity could occur - be accepted by - even be INITIATED by - any protected female whenever she wanted to.
Men liked the spontaneous sex, and the "unprotected" sex.
And the social pressure on women for the attention of men became pretty acute. The girl, on The Pill, who put out was popular. The girl who didn't was a prude. Remember, in the 1960s there was no AIDS and nobody had ever heard of herpes, so why NOT?
For married couples, it was viewed as a "godsend": spontaneous sex, whenever you want it, without the consequences of huge families difficult to maintain on middle class incomes. To quote Loretta Lynn: "The Pill might change the world tomorrow but, meanwhile today, here in Topeka the flies are a buzzing, the screen door's a bangin' and the floor needs a scrubbin', one needs a spankin' and one needs a huggin', Lord, one's on the way...(O gee, I hope it ain't twins again)".
Birth control, at FIRST, ended the baby boom by allowing married couples to have sex all the time WITHOUT children. The morality didn't fail immediately. First it was primarily the marrieds using it.
But then things started happening. There was always a DEGREE of people sleeping around, to be sure. But there was always a RISK associated with that. The Pill removed the risk. MORE people slept around, and therefore got caught, and there were, naturally, more divorced. Also, the single girls found out pretty quickly that if they put out, they got a lot more male attention. Now, of course they DID still get married (the world did not change overnight), but they had had quite a time with several sexual partners before marriage, something far too risky before The Pill. Men and women became expendable to each other. Of course, then, divorce needed to be made easier.
It all flowed from The Pill, because the pill made sex conasequence free for 20 years. Then disease set in. And now, collapsed birth rates.