Saying "the only way" the world gets worse is if we don't have children is to ignore the potential for all of those effects to grow worse. It's certainly possible that we may overcome them and human life will continue on its merry way, but it's very unreasonable to ignore all these difficulties and the psychological effects they can have on new parents.... And on new children.
What would your response be to a 9 year old having an existential crisis about the polar bears starving to death because of climate change, and the implications for human civilization, and civilization's apparent apathy towards that? "Don't worry kid, just make sure you have children of your own and everything will work out"?