It's a factual argument. Our civilization has been peaking in agricultural productivity decade after decade for 200 years. Your hypothetical argument is not statistically likely. Sure, on a long enough time frame some natural disaster will occur that causes a crisis, but the fundamental mechanics of photosynthesis and ag science aren't going anywhere.
No, it doesn't. It still levels off way above what was the carrying capacity of Earth before the "Green Revolution" - and the systems maintaining our food production are unsustainable. We extract surplus food from the ground by destroying the ability to grow more food in the future.
