It's indisputable that the number of calories obtainable per acre of farmland is much, much higher for grain and vegetables than for meat, even leaving aside the animal suffering involved. Are there major ecological issues with the way all food is produced in the world today? Of course. But then I haven't seen anyone claiming otherwise. Have fun with your straw men.
What is also indisputable is that gigantic tracts of non-arable land produce meat.