You're assuming a pound-for-pound, calorie-for-calorie equivalence - that humans could eat 100% of the biomass consumed by animals (and would, with other option

You're assuming a pound-for-pound, calorie-for-calorie equivalence - that humans could eat 100% of the biomass consumed by animals (and would, with other options available). This is obviously not true. Much of what we feed to animals - corncobs and wheat hulls, for example - is inedible to humans. Most of the rest requires extensive processing to be edible. Corn and soybeans are fed to humans mostly in the form of factory-processed junk food, not as fresh vegetables. The human population has more than doubled since the 1960s. This is due to a massive increase in food supply. Increased meat consumption is a side effect of this luxury. The root problems, to address your concerns, are not meat - they're pump-driven irrigation, diesel-powered tractors, nitrogen fertilizers, chemical pesticides and herbicides, and all the other things that have both increased the arable land supply and increased the productivity of that arable land.