Something the anti-meat people might forget is that the majority of plants by weight is going to be cellulose which is something indigestible by humans. You can

Something the anti-meat people might forget is that the majority of plants by weight is going to be cellulose which is something indigestible by humans. You can feed some animals with the waste plant material (or with plants that can be grown more efficiently than human edible ones) and then eat them. The flexibility here gives you options and options are important for maximizing efficiency.