And if we went back to living in caves, I'd take up eating animals again. I used to hunt, and I have no particular qualms in taking it up again if it was necessary, which is more than I could say for a lot of people. I always found it incredibly hypocritical when non-vegetarians used to criticise me for hunting.

We are perfectly capable of eating a plant-based diet, we can derive any missing vitamins (e.g. B12) from supplements and fortified foods. Most of us have the choice to forgo eating animals.