While the argument is not implausible, the secularisation is part of such a huge societal change that it imho difficult to argue causation. A ton of things are

While the argument is not implausible, the secularisation is part of such a huge societal change that it imho difficult to argue causation. A ton of things are changing about our societies, among them secularisation and drops in childbirth rates, is a more conservative view. For example, increasing female access to career development probably drops child birth rates. Is that in itself driven by secularisation? I don’t think directly. And indirectly, everything is related.