Procreation is only one ingredient. Europe (and the US) has to come to the realization that a Secularist government is too weak to survive. Christianity has been actively and calculatedly suppressed in the way that Christianity is most vulnerable, from argument and advocacy in the public square. Islam is not vulnerable in this way. It spreads through governments by the sword with far more pragmatically disingenuous and brutal methods to gain and retain "followers".
The funny thing is, Secularism was only allowed to reign because of the goodness of Christianity, which does not strive for power in governments or special consideration in law. Islam, however, has no such restraint, and Secularism is in no way capable of withstanding the onslaught of a brutal power-seeking religion (that ironically, Secularists characterize Christians as being). Christianity is capable of and has overthrown Muslim rule and changed the hearts and minds of millions of Muslims through peaceful means. It is like we are in the middle of a large game of Rock Paper Scissors, and we're going from Secularism beats Christianity (by exploiting Christianity's goodness), to Islam beats Secularism (by exploiting Secularism's weakness), and in the future back to Christianity beats Islam.
See my #120