Years ago, when I (started and) ran the Boston Vegetarian Society, I invited comparative anatomist, Dr. John McArdle, then Scientific Director of NEAVS, later Scientific Director of the Humane Society of the United States, to speak on the anatomical argument for vegetarianism.
Dr. McArdle was then a lacto-vegetarian for ethical reasons.
Dr. McArdle's conclusion, after walking us through the anatomical argument for vegetarianism, was that the idea is faulty for a variety of reasons (which he listed!).
So, for specific reasons, he rejected the argument IN FAVOR OF ethical arguments for vegetarianism. Ethicists like to consider the relative legitimacy of each of the arguments offered against or in favor of a point of view or course of action, and if outcomes (vegetarian practice) are to be sanctified (as consequentialists/utilitarians wish to do), then due diligence (prudential reason) brings us to seriously and systematically consider whether or not there is utility in arguments that only a few believe (e.g. how many go vegan because of 2-3 naked 20-something coeds on vegan diets, whatever their motivations?).
I want to cite a great Israeli philosopher, Dr. Nir Eyal of Harvard:
"For the consequentialist, consequences are everything - EVERYTHING!" Consequences (of a course of action/s) is the same as results or outcomes.
So, one MIGHT say that questionable arguments (or even good arguments) are 'good' (according to the consequentialists) to the extent that they effectively motivate thinking folks who consider them towards the desired or desirable actions or course/s of action. By this account, one COULD argue that faulty arguments are 'bad' or undesirable to the extent that they yield undesirable results (in motivating behaviors). Of course, should behaviors be decided on the basis of ethical arguments? What is the status of ethical arguments.
Dr. Randall Collura (PhD, Biological Anthropology, Harvard, 2006), a lifelong vegetarian (now a vegan) ALSO gives a talk on this topic and reaches conclusions like that of Dr. McArdle, that the anatomical argument for vegetarianism is invalid because it's (a) logically faulty AND (b) is contradicted by the facts (which likely were NOT evident to those who developed the argument, when it was developed). It may seem persuasive to some, but it fails falsification tests. Remember that the anatomical argument for vegetarianism is NOT an ethical argument; it is purportedly a descriptive claim about the propriety of the feasibility of nourishing ourselves on botanical foods ONLY.
The more widely held view today is (a) that we humans are omnivorous BUT (b) that we are NOT 'obligate carnivores'. We do not NEED to eat meat to survive or thrive, but we are ABLE to derive nutrients from all manner of soft tissues - from animals or from plants.