Look at Japan right now to see where any other country will be in ~30 years. The declining birthrate has resulted in an unstable top heavy population full of old people dependent on the few young people. Which leads to more strain on young people, which means a lower birthrate. Which leads to more old people vs young.
The risk isn't the pure population number, it was great 50 years ago because everyone was young, it's the distribution of the age in the population.
But somehow people want to disagree with each other so much this is labeled a right wing talking point because conservatives encourage having kids. No, we need kids, and now all of them are going to be raised by conservatives.
Idiocracy becomes less of a meme and more of a documentary every year.