I was hearing an interesting podcast on this subject recently by a demographer. This man is completely secular, so he has no problem with contraception on a moral level, but he was just explaining what is happening now that people have almost stopped having children.
First of all, when a society's birthrate collapses, it takes several decades for anyone to notice. The reason for this is that it takes 20 years at least for a newborn to enter the workforce. So right there that's 20 years before there is any labor shortage. But then most people continue working until their mid-60s, so the last large generation of people are going to keep working for 40-50 years before they retire.
I'm sorry, I'm having a little trouble explaining this, but here's the point: When you get to the point where it's 60 years since the last large batch of babies was born, that batch starts leaving the workforce through retirement, and the labor force starts to plummet. That's what's happening now. The most fertile year in American history was 1958, in which each woman had an average of 3.6 children. The replacement rate for a population is at least 2.1 children per woman; the last time this country saw that was 1972. The last decade hovered around 1.7-1.8
Now, someone born in 1958 is 64 today. He is just turning 65, the typical retirement age. And he is the last of the boomers. By the end of this year, every Boomer will be over retirement age. Since Boomers didn't replace themselves, that means there are a lot fewer people available to replace them as they retire, than there are Boomers retiring.
I suspect this partly explains the current labor shortage in this country, among many other things. But the point is, the labor shortages are inevitably going to get worse and worse, as each generation is smaller than the previous, and many jobs are going to be left unfilled. Hopefully with automation this lack can be mitigated, but the future of civilization is not looking good as this country's population ages.