Thank you, everyone, for your answers. I appreciate it very much. However, I still have a question. What would happen if no one used contraception? How would we all “fit” on this planet? With advances in medicine and improvements in health care, people are able to live longer and be cured from diseases of which there were previously no cures. Many women do not have regular menstrual cycles, so NFP is not a reliable alternative for them. Since the only other alternative is abstinence, this would mean that a married couple should not have sex if they choose not to have multiple children; abstinence in a marriage would be a sin as well…
This hypothetical is so far removed from the present reality of the world that it’s hard to speculate in exact terms. Some things to consider are this:
Contraception is sort of the last milestone in a holy marriage. There are very, very few people alive who would morally object to a contraceptive but wouldn’t morally object to, say, fornication, among other areas of sexual ethics. So in your scenario, if we suppose that we lived in an orthodox paradise, and the entire world refrained from contraception, then we would also have to presuppose that the entire world refrained from adultery, fornication, divorce, prostitution, in vitro fertilization, etc. So all the channels of bearing children through illegitimate means would be gone. All of the channels that create near occasions of sin and needless temptations would be gone. It would presumably mean that vocations as generous singles, religious orders and the priesthood would be dramatically higher (celibates). It would also mean, as per our modern world, that people wouldn’t generally be getting married as teenagers, as was often the case in past centuries, but much later in life. When you put that together, I really don’t think the birthrate would be as high as you might think.
Of course, we don’t live in that kind of world. Not even close. When you consider the negative birthrate in several regions of the world, Catholics having large families is simply going to counteract it. Current predictions is that the population is going to top off at around 10 billion people and then start declining somewhat.
We also have no idea what kind of technologies and methods will be used in future generations to sustain ourselves. It’s a regressive kind of thinking to believe we won’t be better at it than we are today (when all evidence is to the contrary).