Literally any doomer mentality is generally considered unpopular the more you elaborate on it. Even if it starts popular.
For example: I would like to explain why I think we need less people. That sounds agreeable. We need less people urgently tho. It's the fundamental, foundational reason behind a large part of the world's problems. That is still... somewhat... agreeable, But.... But. But but.... solving it? And there we go, because see, there's only three methods to actually achieve it, and every single one of them will get people mad about this thing called "human rights" if we deem any of method worth trying.
So yeah, we're doomed. Humanity is going to land on a critical point of failure in 300 years.
Solve it by raising the worldwide standard of education and quality of life, because that's proven by far the most reliable method of controlling the birth rate.
I've yet to hear anybody complain or disagree with that approach.