While it might seem odd, the debate over the ethics of eating meat is an ancient one, going back at least to Pythagoras. Pythagoras appears to accept reincarnation, so a hamburger you eat be from a cow that had the soul of your reincarnated grandmother. Later philosophers tended to argue in defense of eating meat, although they took the issue seriously. For example, Augustine considered whether killing animals might be a sin. His reasoning, which is still used today, is based on a metaphysical hierarchy. God created plants to be eaten by animals and animals to be eaten by humans. This conception of a hierarchical reality is also often used to defend the mistreatment of humans. Saint Thomas also considered the subject of killing animals, but ended up agreeing with Augustine and arguing that the killing of an animal is not, in itself, a sin.
There are philosophers who argue against eating meat on moral grounds, such as Peter Singer. These arguments are often based on utilitarianism. For example, it can be argued that the suffering of the animals outweighs the enjoyment humans might get from eating meat. This argument does have some appeal, for the same reason that arguments against murdering humans for enjoyment can be appealing. There are also arguments about eating meat that are based on practical considerations.
One category of practical arguments in favor of eating meat is based on concerns about health. Some people argue that a person cannot get enough protein from non-meat sources; but this is patently untrue: there are many excellent non-animal sources of protein such as beans, peas, and quinoa.
A better practical argument is based on the difficulty of getting essential nutrients from a purely plant-based diet. For example, getting enough iron is a problem. But the nutrient issue is relatively easy to address by using supplements and fortified foods—something meat eaters also often do. So, while eating a healthy non-meat diet can be challenging, it is not exceptionally difficult nor is it unusual—after all, even meat eaters often face the challenge of getting all the nutrients they need. But this is a reasonable practical concern.
In addition to the moral and practical arguments for eating meat, there is also a rhetorical tactic of characterizing eating meat as manly and eating plants as weak. The implied argument here is probably that men should eat meat because otherwise they will be perceived as weak rather than manly.
Various evolutionary explanations have been offered for this perception, such as the idea that when humans were hunters and gatherers, the men did the hunting and the women did the gathering. But women presumably also ate meat while men also ate the gathered foods. In any case, what our ancestors did or did not do would not prove or disprove anything about the ethics of eating meat today.
As one might suspect from the idea of a “Manly Meat Argument”, sexism is often employed in this rhetoric: vegan or vegetarian men are not manly men and perhaps “might as well be women.” This is, of course, not an argument to prove that eating meat is morally good but an ad hominem attack, probably intended to shame men into eating meat.
Another common rhetorical tactic is to mock vegans and vegetarians by unfavorably (and mockingly) comparing hunting animals to “hunting” plants. The idea, one infers, is that hunting an animal is a dangerous manly activity, presumably worthy of praise. In contrast, “hunting” plants is safe and unmanly, presumably only worthy of mockery.
Those using this rhetoric probably do not realize that they are also insulting farmers (who are usually praised by these same people). After all, this rhetoric implies that farmers are unmanly and should be mocked for growing plants.
Having grown up hunting (and fishing) I know that hunting does involve some risk; but the #1 danger in deer hunting is falling from a tree stand (wisely, I always hunted on the ground) rather than being wounded in an epic battle with an animal. While I would respect the prowess of someone who could take on a buck in hand to hoof combat with nothing but a knife or spear, modern weapons make killing animals ridiculously easy. That said, hunting does require skill, but so does farming. Farming requires battling pests and the elements, so it seems odd to cast it as “unmanly” and mock it.
The manly “argument” becomes absurd when made by people who buy their meat rather than hunting for it. After all, the danger faced when buying a steak is the same as that of buying tofu. Since I grew up hunting in the Maine woods, when some fancy lad (who would be killed and eaten by raccoons) makes the manly meat argument on the internet, I must laugh at them. That said, this criticism does not show that hunting meat is not more manly than gathering plants—it just shows the absurdity of people who buy their meat mocking vegans and vegetarians by unfavorably comparing hunting meat to gathering plants.
But perhaps the manliness of eating meat is not about having the skill to track and defeat an animal in the wild, but it is about the suffering of the animals. That is, eating meat is a manly gesture of cruelty and a lack of compassion. Factory farming is a moral nightmare of abuse and suffering. So, perhaps eating meat is for hard men while caring about the suffering of other living things is for soft ladies. On this view, the cruelty is the point and that is why eating meat is manly. Ironically, this would seem to be an immoral argument for eating meat—people should eat meat because doing so supports cruelty.
It could be countered that there are ethical ways to raise animals for food—free range, cruelty free and all that. But the risk of this sort of reasoning is that it acknowledges that the suffering of animals is wrong and moral consistency would seem to require that one give up even this meat—after all, an animal must still be killed before it would naturally die. But it is reasonable to think that the treatment of the animals prior to their execution is morally relevant to the moral issue. But this would not say anything about the manliness of eating meat and might seem less manly to eat meat resulting from less cruelty.
I do understand there can be times when survival requires killing and eating animals and a good moral case can be made for doing this. I also get that some people need to hunt for their food; they are certainly not to be condemned. But this is distinct from the manliness of eating meat.
While I get the concern with defining what it is to be a man, I am inclined to think that it is not fundamentally a matter of what one puts in their cart at the grocery store or orders at Taco Bell.