We already have an abundance of natural resources (at least... for the developed countries) The problem is that they aren't evenly distributed enough, to the extent that a lower population cannot counter the increasing wealth inequality.

>to the extent that a lower population cannot counter the increasing wealth inequality.

Wealth inequality has nothing to do with it; some of the countries with the lowest wealth inequality like Northern Europe have the lowest birthrates. A hundred years ago wealth equality in most countries was much higher than now and people were much poorer, yet they were still having many more children than people today.

  We already have an abundance of natural resources (at least... for the developed countries)

You can blame the billionaires who own the vast majority of the wealth but that's mostly due to the stock market giving them that value on paper. Physical resources stay finite.