People have claimed humans couldn't sustain themselves for hundreds of years now, yet we have grown, and made major advancements to support more people. The air in many parts of the world is cleaner now than they were just 20 years ago, water is cleaner in many parts of the world than 30 years ago, etc. It's not like humans are stagnant. Things are actually getting better for most people on earth. Less poverty, less war, less hunger, less disease.