Earlier quoted context omitted.
But will the membership decline continue in the long-run? Within the Catholic church, there is a traditionalist/conservative minority, who are growing basically through having a high birth rate – rejecting contraception and pre-marital sex, they tend to marry young and have lots of kids. Not all of those kids will follow in their parents' footsteps, but the majority of them probably will. Though these conservatives/t…
Europe has entire countries where pretty much 100% of the population were extremist Catholic zealots with huge families by modern standards just a couple of hundred years ago. Today those countries have some of the lowest birth rates in Europe, e.g. Spain and Italy[1] pretty much trail the pack. The data suggests that your hypothesis is false. 1. https://en.wikipedia.org/wiki/Demographics_of_the_European_U...
And should big families in Catholic-majority countries 100-200 years ago be attributed to Catholicism? Well, other countries, with completely different religious beliefs (e.g. Muslim-majority countries, India, China) also had big families. Most people back then, whatever their religion was, had big families due to primitive contraceptive technology, high infant mortality, economic value of child labour, less years spent in education, lack of educational and career opportunities for women, etc. Nowadays, there is a correlation between religiosity and family size, but that link is historically novel; for most of human history, the devout and the non-devout had big families alike.