Can you explain what you mean with 'psychological effect'? And what exactly of eating the flesh of another animal makes you human. I can understand our ancest

Can you explain what you mean with 'psychological effect'? And what exactly of eating the flesh of another animal makes you human. I can understand our ancestors having to hunt and kill animals to survive. But I don't think modern society needs to kill so many animals (billions) and destroy the environment to survive. It's a rather inefficient way to feed the world.