I have heard both sides of the argument on the B12 issue — whether or not the plant-based B12 that is found in sea vegetables, fermented foods like tempeh, algaes like spirulina and chlorella, yeasts, and even some organic vegetables, is in fact bioavailable and can actually be digested by the body. There are certainly contradicting studies (see http://www.pamrotella.com/health/b12.html for an excellent article presenting both sides of the coin), though most of these studies agree that the real source of B12 is actually bacteria (whether it is in an animal or in the air we breathe on the subway). I am not a doctor, but from my own experience of being a vegetarian for 15 years and completely vegan for 9 years, I have never had any tests come up showing low or anything but healthy B12 levels.

Outside of eating the above listed foods, concerned individuals can also consume foods which are fortified with B12, as extra insurance — like some juices, bread, cereal, protein powders, etc. Or, there are plenty of vegan supplements which easily provide B12 without having to resort to eating meat. We only need a microscopic amount of B12 each year to keep us in balance (I’ve read our yearly allowance wouldn’t even fill a thimble), and I don’t believe there is any nutritional issue that “forces” us to continue eating animals. Thanks again for your thoughtful comment.