There's also the interesting fact that my parents raised 7 children on the same amount of resources that most people raised 2; we were _way_ more efficient per capita than most households. Oddly enough, we were raised to be more resource efficient than most people. We knew resources were scarce, so we tried to be more efficient. Maybe the solution is to have more children, not less, then teach them to find solutions to any problems encountered. Heck, mine the moon if you need more resources, invest in hydroponics for food if you run out of space, don't start getting rid of the poor people. Then you'd just end up with a bunch of rich folk sitting in panda refuges.
EDIT: I only bring up the last sentence because the question always encountered when someone says "There are too many people." is "Who do you think we should get rid of, how and when?"
EDIT 2: I do agree that we should do better with taking care of the environment and avoid catastrophic issues from bad decisions, and I agree with the post below about both being able to be right. :D
In my short lifetime I've seen drastic changes. I've been to many countries and to many national parks. I've seen the degradation and I know it constitutes anecdotal evidence. In the 70s things were not so bad. Now, it's terrible. Trash a much more common sight in the ocean and in reefs. Micro plastics everywhere. Deforestation. We have room, we have food but soon we won't have a decent place to live in. It'll be too polluted
I'm not smart enough and don't have enough moral insight to be able to determine who should be gotten rid of as you put it. That's too great a power for me to responsibly wield. I don't think anyone should be gotten rid of. I think people should breed less. But even though I haven't enough insight to say how to get to the desired outcome, less people, I know that it's the outcome we need.
The first definition refers to a population so large that resources get depleted so much that the population crashes. The canonical example is lemmings.
Another definition refers to a population so large that it causes widespread harm to the ecosystem.
So it's a myth by the first definition and a reality by the second.