Unless you’re saying most Romans actively disbelieved in gods and/or rejected their observance that’s not what I meant (I used the word ‘areligious’ idiosyncratically but dont’ necessarily want to try to define it now). China might be a better example since the leading traditional religion isn’t really.

I was mainly thinking of a) ex-Soviet style states where decades of officially sanctioned and often coerced atheism seems to have had a devestating effect on social relations that are nowhere near recovering yet.

I’m also thinking of ‘post religious’ western european societies which are actively failing demographically (if a society can’t be bothered to reproduce at around replacement level it’s a failure and will be replaced by one that does). There are also more religious societies facing demographic collapse but I can’t think of a mostly non-religious (another term I won’t define right now) society that’s succeeding at a society’s first task : reproduce at a level needed to keep the society going.