I think it has always been. It's just that the name was invented relatively recently, as well as many unusual things. They were always there, but they didn't talk about it. And in today's free-speaking times, people began to pull themselves up and declare themselves and their preferences in life, look for people with similar interests and even unite in various movements - this is interesting, it is fashionable, this is a chance to communicate with someone with the same interests and views. I never wanted children - I love cats and my hobbies more. However, I only found out about the fact that I am called childfree a couple of years ago from the Internet) But I didn't want to - as long as I can remember, in those days even the Internet did not even exist.
First, there are not always conditions for the birth of children. Of course there are those who give birth no matter what, but childfree are well aware that a child is:
-costs. (big. "bunny-lawn" sayings do not work here, let's think logically - if the family does not have their own living space, savings
then they will count a penny. Why give birth then?)
-the figure deteriorates, the condition of the hair, nails, etc. worsens.
Many people understand that they are not ready to sacrifice such resources for the sake of a child who then he can give up again.
Childfree do not see procreation as the highest goal. They live for themselves, enjoy life, want to learn, travel, develop, create something, while the child, for the above reasons, simply will not let them live as they want. It will not be a joy, but a burden. In this case, the birth of a child will ruin the life of both the parents and the child.
But childfree can treat other people's children quite well, love them. It's just that their life scenario is not the same as that of the others, they chose a different life.
Procreation is one of the most ancient instincts, otherwise the species would simply die out. But childfree couples often have animals instead of children. Believe me, all kittens also need care, and there is a lot of trouble with them. As a childfree I tell you this)
The original wording of the question was not about the history of the Childfree movement, but about the reasons for its origin. In my opinion, the first prerequisite for its appearance was the invention of oral contraceptives by Karl Jerassi in 1951.
You assume that the reason for having many children in pre-contraceptive times was "a natural instinct and craving for motherhood", which for unknown reasons in the last hundred years have disappeared for many. However, we cannot assert that women of past generations gave birth to many children because they had a stronger maternal instinct for one simple reason: they simply did not have a choice. Most women, prior to the advent of affordable contraception in the mid-twentieth century, simply did not face the existential choice of "giving birth or not giving birth." More precisely, the refusal to become a mother automatically meant a complete renunciation of sex life, such was, say, the lot of nuns. Religious morality forbade the already highly unreliable methods of contraception that were known to people. Abortion was a criminal offense.
In this situation, married women had absolutely no opportunity to control the process of childbirth, and besides, the patriarchal way of life did not offer them any alternatives to family and motherhood. The woman did not have the opportunity to realize herself neither in the profession, nor in art, nor in science, nor in politics, anywhere except her family. Not at all these days.
Today, when, thanks to affordable and reliable contraception, sex life is almost completely separated from childbirth, women have a choice and it is not surprising that many use it: some women are limited to having an only child, others they postpone this event to an increasingly later date, and the third, having received the opportunity not to give birth, decide not to do it at all.
Chile free appeared when people stopped constantly living tomorrow and decided to live for themselves, but the threshold for entering life without worries is very high, and in order to live for yourself you need to move your brains, just work and constantly be in trend. And children can take away not a small part of life, and for many they become its meaning.
For some it is acceptable, for some it is not. The latter are called childfree.
Your statement in the direction of people who support this movement, calling them stupid, looks naively arrogant, since calling people who have abandoned children stupid, you mean that you and your children will be what that's good. I doubt this because the chances that your child, like the child of any other person, will be useful to this world is very small.
I would like to add that people have long been able to overcome instincts, we are still not primitive animals, but very logical creatures capable of making decisions based on the experience of loved ones and people living before us.
Not everyone has a natural instinct and craving for motherhood. And you don't need to call men "stupid", if you are not lucky with your partner, then you should not generalize;)