Except, as I said, some previously productive regions were eventually destroyed for good. As I also said, we have only been doing this (modern way of farming)

Except, as I said, some previously productive regions were eventually destroyed for good. As I also said, we have only been doing this (modern way of farming) for a miniscule time span. We have no indication whatsoever that it can go on indefinitely. Starvation has happened in the past, so you are simply fooled by your even more miniscule life span in which you didn't experience war or starvation into an unwarranted optimism. It's also not a given that we will have unlimited energy - that science fiction novels exist with that scenario is not proof. Even desalination might have issues, apparently atm they also cause environmental issues. And water is not the only resource needed for farming. Obviously with unlimited energy you could produce lots of food (for example underground or where ever). But we don't have that.