Religion isn't the only thing becoming extinct in those nations. Go to Wikipedia and search for "Demographics of X " where X is a nation from the list given in the above-linked article: Australia, Austria, Canada, Czech Republic, Finland, Ireland, the Netherlands, New Zealand, and Switzerland. (Nation/ Total Fertility Rate) (Australia/ 1.97) (Austria/ 1.41) (Canada/ 1.58) (Czech Republic/ 1.49) (Finland/ 1.85) (Irela…
But in general better education leads to more wealth, more time spend in schools and those who have college degrees are less likely to be religious and they are less likely to have children (the price of kids is low if they can help out on the farm, very high if you have to raise them in a modern society).
I don't know a good solution to this, but I suppose the problem with fix it self on way or another.