Population decline is only a concern for pyramid scheme economics boosters, and is sold to the public based upon fear mongering nonsense that doesn't hold up to scrutiny. In many ways population decline could be a panacea.

The population explosion, on the other hand...well we've already baked in extremely severe consequences, and people are learning that when you have more vying for the same, there are consequences.

One is a legitimate, extremely severe problem that is going to cause enormous harm to humanity. The other is fake.