From Population Growth to Declining Birth Rates. 
The Population Bomb, a 1968 blockbuster book by Paul Ehrlich, taught that society’s biggest threat and harm was the geometric growth rate of the population. According to Ehrlich there were too many births, too many people for the good of the environment and the economy. The modern era, beginning somewhere around the 1950s has been one of limiting family size. Many believe, like Ehrlich, that the population is too large. Today, although population growth continues for the time being, a long-standing trend of declining birth rates brings new concerns for humanity.
There are several main reasons why birth rates have begun to decline. Families had been large in the previous, largely agricultural era, since children could be 
farm laborers and were viewed as a positive. In the new era, children began to be viewed as a negative; they had to be entertained, cared for, and educated. The arrival of feminism taught that they were a hindrance to the self-development of mothers who should really be in the labor force. The availability of prophylactics meant that couples could avoid having children, and many did just that. The sexual revolution had similar causes and effects. Sexual satisfaction became decoupled from both marriage and human reproduction. Cohabitation and promiscuity were no longer inhibited by the potential hazard of the arrival of an unwanted child.
For the child still arriving unexpectedly, the later phenomenon of mass legal abortions has been seen as a means of constraining population growth. But now the birth rate has fallen below the rate required to maintain the population 
at the current level. We have come to the recent recognition of demographers and social scientists that populations not only grow with geometrical rapidity, but also decline the same way. Today, the advanced countries have birth rates too low to offset deaths and national populations have begun to decline.
I can remember forty years ago teaching that in a century from that time, the German nation will have declined from about 80 million to 10 or 15 million, all of which would be descendants of the Turkish people who came as guest workers to Germany. On March 17, 2017, Turkish president Recep Tayyip Erdoğan called on Turkey’s European citizens to increase their rates of procreation and have five children each. He insisted that a booming Turkish population would be the best answer to the EU’s “vulgarism, antagonism, and injustice” (so reported the UK’s Telegraph). He is convinced that within a few decades Europe will belong to the Turks.
The Economic Problems of Demographic Winter
Consider just a couple of problems that will arise with falling populations. The housing market can accommodate families considerably larger than the one or two children standard of the recent past. And houses have been built for a substantial population, but what will happen when the baby boomers of the post-World War II era and the declining population to follow them want to downsize and put their larger than convenient homes on the housing market. In the future there will be a large glut of such homes on the market as there will be increasingly smaller cohorts of buyers to purchase them.
When social security was introduced there were about sixteen people in the labor force to provide the goods and services for one retired person. Social security is not an insurance program in which one’s continual contributions are set aside as savings for that person’s retirement. It is simply a transfer program where the money people pay in (if not confiscated by politicians for other purposes) is transferred to people currently retired. With a declining population we will discover that we now have only three or four people contributing to the retirement of each retiree. In the future we will see yet fewer contributors for each retiree. Ever fewer workers will not be able to sustain the growing number of retired persons they would need to support.
Other Problems of Declining Populations
The economic problems won’t be the worst of societal difficulties once an increasingly rapid population decline begins within few decades. It turns out, according to social scientists, that children who do not enjoy the benefits of the nuclear family do not gain the concern for others, the normal development of skills valued in the market place, or the cognitive stimulation and development that occurs in families. Many different kinds of statistics describe serious problems that children without siblings encounter in their development. When they fail to gain the social and developmental skills needed, many are unable to contribute productively to society and become candidates for welfare statism. One of my recent blogs on the increasing death rate of whites over 25 years of age indicates the issues already arising for much of the American middle class.
Jesus Christ prophesied of our time when He said “the love of many shall wax cold” (Matthew 24:12). Those who use their sexuality only for personal 
gratification and who live only for their own personal goals and aspirations can easily be alienated from other people. Siblings of families learn to care for others; even if they sometimes don’t get along as well as their parents would hope, they later become parents and care for their own children. Cold hearts will mean loneliness for many children. Those who develop poorly view governments only as institutions to provide for their personal needs. They may easily find socialism appealing because it permits them to think they are championing the interests of others. But they feel no personal urge actually to give back or to be involved in service to those around them. They often seem more interested in being on governmental recipient lists.
Socialism is the personal philosophy growing out of the economic and cultural conditions developing in Western society. It gives lip service to the welfare of everyone, but hearts of people are locked on their own incomes and future prospects for income and wealth. Socialism is mostly self- concern. In the United States, socialist policies have promoted many of the activities and attitudes that have resulted in declining birth rates. Promotion of abortion, of denigration of women choosing motherhood rather than labor force participation, and promotion of the idea that environmental damage is a function of excessive population are common ideas for socialists.