Reason alone is never enough to make people do right rather than wrong.
A felt, empathic component is necessary too, so you feel why it’s right or wrong.
Sam Harris seems to have some, but not yet enough, of either (the reason or the feeling).
It is definitely not rational to start eating meat again because you develop an anemia, rather than to check why you got the anemia and do something about it.
(A B12 and B6 supplement, or a more balanced choice of plant-based foods would definitely have fixed the problem — and, to be rational, Sam Harris should have looked into that and done it from the very beginning.)
The felt, empathic component is still weak too, otherwise Sam would have had the motivation to look at causes and alternatives rather than going back to eating meat.
Being just a vegetarian is also not what is dictated by reason — nor by feeling. The dairy and egg industry are a part of the meat industry and cause horrific suffering. (mMilk-givers and egg-layers are all eventually killed for meat, and so are all their young, except the ones kept for milk-giving and egg-laying, and their lives are short and extremely wretched).
Vegetarians are also continuing to eat animal protein, which keeps their metabolisms dependent on and desirous of meat. Once you become completely vegan, your metabolism changes, your appetite for plant-based food increases dramatically, plant-based food becomes much more tasty and much more efficiently metabolized, and your appetite for meat disappears.
So any yearning to start eating meat again is gone, and if you discover you need to take more of some supplement — like B12 or Calcium or D2 or iodine, or omega-6 — you just go ahead and take the supplement instead of using it as an excuse for going back to meat eating.
Richard Dawkins seems to wish we all didn’t eat meat, and thinks we will one day look back on it as having been as awful as slavery. Yet he still eats meat. A speaker as prominent and influential as him could do a lot more good for animals if he set the right example. Rationality would seem to dictate that too.
On Noam Chomsky on animal rights:
The notion that only those individuals who have responsibilities can be accorded rights is irrational, since we accrod rights to bot infants people who are severely ill or handicapped. But instead of thinking it as our according rights to victims, we can think of it as all of our having obligations not to cause any feeling being needless suffering. This has nothing at all to do with whether the victim of the suffering has responsibilities.