That's a false dichotomy. These days we put so many nutrients artificially into the feed of livestock, e.g. B12, that we might as well skip the whole livestock

That's a false dichotomy. These days we put so many nutrients artificially into the feed of livestock, e.g. B12, that we might as well skip the whole livestock step and just take a vitamin pill every morning. Most people have a vitamin-D deficiency, most vegans that I know of at least take care of making sure that they get enough supplements.