So? Human society and culture can change absurdly fast. If the evolutionary impulse to reproduce was that strong, you wouldn't be seeing places like Singapore with comically low birth rates.

What evolution compels us to do is have sex. We've just disconnected that from reproduction.

Re:mormons, yes they have a higher fertility rate, but it's also been rapidly dropping. And without taking into account conversions/apostasy the numbers are kind of useless, and taking them into account is difficult because it's just inherently hard to predict. As an ex-mormon I'm aware that the internet has caused some major problems with retaining members for the church, because information has become so much more accessible (much of it contradicting church teachings, obviously).