You aren't growing food in deserts, Arctic tundra and don't want to cut down rainforests.

Even now there are people who can't afford food, the more efficiently farming is done, the cheaper food will be for them.

Not all land is the same. But I don't think it's about land use. It's about water usage, soil and water contamination, deforestation, greenhouse gas emission and the inefficient conversion of plant calories to animal calories.

Oh and of course the tiny little detail that applying the efficiency optimizer that is capitalism results in atrocious treatment of sentient beings (pardon the pathos, feel free to substitute with emotionless words if you can think of any).