USA Today had a great article last week on the relationship between the de-Christianizing of Europe and it’s declining population growth.  Is God Dead in Europe contains interesting facts and factors:

Among the consequences of Europe’s abandonment of its religious roots and the moral code that derives therefrom is a plunge in its birth rates to below the replacement level. Abortion, birth control, acceptance of gay marriage and casual sex are driving the trend. Europe is "committing demographic suicide, systematically depopulating itself," according to Weigel. 

United Nations population statistics back him up.

Not a single Western European country has a fertility rate sufficient to replace the current population, which demographers say requires 2.1 children per family.

Europe is showing us where this path (secularization) leads.

Of course, the author really hasn’t made the causal link between all those -isms and population declines, but he is making the accusation, and I assume others have the data to back this accusation up.  It’s not too hard to see how abortion, birth control, and the devaluing of larger families leads to less children. 

Europe is certainly leading the way to self-destruction in it’s pursuit of secularism.

Contrary to the expectations of the Enlightenment, freeing individuals from the shackles of traditional religion does not result in their moral uplift.  To the contrary, the evidence now shows clearly that "no society has yet been successful in teaching morality without religion."
– Guenter Lewy, Why America Needs Religion