Earlier quoted context omitted.
It is such an unpopular opinion but this is the answer. Humans are selfish. The earth can't sustain 8B+ people. Maybe 2B max with some technological advances for cleaner cars and other renewables.
It is rightfully unpopular, because it's not based on facts. The earth could easily sustain 8B+ people if certain countries do not over-consume as they are currently. But you are right, people are selfish, especially these over-consumers.
I think it's better for 2B billion to enjoy life, than for 20B to live under some miserable constraints.