I’ll acknowledge that saying it’s a dog whistle every time was slightly hyperbolic. 

However, I’d argue that the claim that the global human population is declining too rapidly is actually pretty hotly contested. The world's population is still growing — around 8.2 billion now, heading toward a peak near 10.3 billion in the 2080s.

That being said, in some countries there will be a surplus of retirees and not enough workers to fund them through the existing tax structure, which is a legitimate problem. But it's a problem best remedied through better social safety nets, not by popping out more babies.

The biggest contention I have with the concern over population decline is that population decline doesn’t matter at all if we don’t adequately address climate change within the next decade. If someone’s house is actively on fire and they express concern to me that their roof should be re-shingled, I’m not going to give a shit about their roof shingles until I’m certain their roof will survive the fire.