Many people, including myself, have called Humanae Vitae a prophetic document. But, as I think about events, I suspect we are all wrong. It is not a prophetic document at all. Let me explain.
Everyone talks about the terrible social lapses caused by contraception. What most people don't realize is that the eugenics movement and its daughter, the contraception movement, were merely steps in an already existing problem. The problem was the demographic transition. The cause, as near as anyone can tell, was the Industrial Revolution and the improvements in housing and medical care that revolution made possible.
The demographic transition, that is, the loss in fertility rate below replacement levels, actually began in the early 1800s. Dropping fertility rates spread from France and England throughout the world, country by country, for the next two centuries right up to the present day. The current baby-bust is not the aberration, the post-war Baby Boom was the aberration.
But, because we all grew up in the post-Baby Boom years, we all think this is a post-1960s problem. It isn't. And, while the Church has never changed her teaching, while the Church has always taught that we should not exploit workers or women, Rerum Novarum, Casti Conubii and Humanae Vitae, were documents that were playing catch-up. The Church was late in recognizing the nature of the problem in the sense that She was late getting a firm grasp of the cultural shift.
The Luddites understood that the machines were going to create a problem. They misunderstood exactly how. They thought machines would take everyone's jobs and make everyone poor. Instead, the machines took most people's jobs, but made everyone rich. They knew there was a problem, but they didn't understand the problem.
Marx saw it as well - he was wrong in an entirely different way than the Luddites. He thought the machines would allow a small group of people to exploit the workers. It never occurred to him that it would allow that small group of people to simply ignore the workers. Again, he knew there would be a problem, but he didn't accurately predict what the problem would be or how it should be resolved. Indeed, he thought the destruction of the family would be a good thing. He absolutely did not understand that the industrialized destruction of the family was the problem. The worker-employer relationship was just a symptom. The central problem completely eluded his grasp.
The Church has always taught that people are subjects, not objects, and the larger Christian society had largely understood this, for over a millennia at least, by 1800. What the episcopate took too long figuring out, in re both workers rights' and contraception, was that Christian cultural attitudes towards those two issues were undergoing such a major and rapid shift that encyclicals were required.
Culture had already gone 70 years down that road before we saw Rerum Novarum, 100 years down it for Castii Connubi and 150 for HV. THAT is the sense in which the Church was late to the table.
Not that anyone else was much earlier - we would be hard-pressed to identify someone who pronounced earlier AND correctly, about what was coming. Lots of people pronounced earlier, but they all got something important wrong. Others got the essentials right, but largely by mimicking what the Church had already said.
The problem is precisely in the fact that, by the time the Church had articulated the problem correctly, in a way the culture was likely to understand, the culture had changed to the point that the Church was largely ignored.
In that sense, Rerum Novarum, Castii Conubii and HV were actually not prophetic at all. They were all three simply descriptive. After all, what those documents described was already well underway - it was just that the Church was the only one who saw it, because She was the only one who was still able to see.