You forget that the food required to make even small quantities of meat is much higher than just growing plants for human. Better to directly eat the energy produced by autotrophs. Deforestation doesn't happen in "poor countries" just so people can survive, it happens because corporations lobby the government of corrupt countries like Brazil so they can destroy habitats for feed and pastures.
Meat production is a simple maths problem to see that wasted energy used by livestock (to survive and grow) is lost energy.