[Anamon]

That's under the assumption of framing it as a problem. Personally, I think naturally declining birth rates are a corrective measure for an already wildly overpopulated planet. And that we can be damn glad that this is the way things seem to be heading, because the alternative would be an ever accelerating freight train heading for one of several much more devastating scenarios of population reduction.

Even with sub-replacement birth rates I don't see humanity at a threat of extinction (from natural population decline!) in the next tens of thousands of years. And even if -- what's the issue? It's only humans who think humanity is this great gift to the universe that needs to be protected and spread.

[Night_Thastus]

It's a problem because there's no evidence the population will ever stabilize. Wild animals form some natural equilibrium based on the available resources, humans do not. If there aren't enough resources we find ways to get more.

If the population dips, it won't add any pressure to have more kids, not on an individual level.

And a lot of humanity only works at scale. Global shipping, for example, only really works at the enormous scales we're doing it at. Same goes for communication networks.

If the population dips low enough, things like that start to break down. If we slowly dipped from our current to say, ~500 million, our chance at being a space-faring race is over. You may think that's a lot of humans - more than enough to accomplish everything. But they'd be spread too thin, with too little demand for industry and innovation to make it work.

Humanity isn't some great gift to the universe now. It's full of selfishness and greed and fear and arrogance and ignorance. But maybe, one day, it could be. I want to believe in that future.