OK, I hope my question doesn’t get misunderstood, I can see how that could happen.
Just a product of overthinking.
Idea is that we can live fairly easily even with some diseases/disorders which could be-life threatening. Many of these are hereditary.
Since modern medicine increases our survival capabilities, the “weaker” individuals can also survive and have offsprings that could potentially inherit these weaknesses, and as this continues it could perhaps leave nearly all people suffering from such conditions further into future.
Does that sound like a realistic scenario? (Assuming we don’t destroy ourselves along with the environment first…)
Well, if that were the case wouldn’t we expect to see near universal religious belief now?
We can’t start the population set now, we should look at when religion started.
I’d posit that as time goes on, the religious beliefs tend to want to spread, but they also round off more difficult to wrangle aspects to maintain appeal to a wider audience. A belief system incompatible with observed reality or unpalatable to potential new believers is going to be less robust than one that fits and is welcoming.
It’s why today’s extremists are generally more tame than the commonplace believers of the past.
Eventually some people catch a version of the religion so weak that it’s only kinda comparable, and you have the Christian who never goes to church or thinks about it really, or the person who’s a vague notion of spiritual without much specific behind it beyond a vague notion of purposeful intention to the world.
I’m not talking about converting new believers from outside, I’m talking about children inheriting the religion of their parents. And yes, in the places where religion has spread, only a small percentage of the population wasn’t religious, and it’s a relatively recent thing that a significant fraction of society isn’t religious.
But we still see a trend line of decreasing religiosity and a taming of extreme religious beliefs.
Children are way more likely to take the religion of their parents than otherwise, but they’re still new believers that the idea has to be able to take hold in, and if the idea just doesn’t fit then you’ll see a departure. It’s not like their religion is the only one trying to take root.
I just don’t think we see the world today that we would if religion spread with the force of population dynamics.
We see majority religions like Christianity decreasing, but minority religions are actually increasing, at least in the US.