Good contributions so far, although I take issue with many of the arguments put forth, not in themselves or for the individuals, but in the context of parlance with vegans. All of this circle of life, natural food chain, natural order, appeal to tradition, naturalist fallacy stuff is a non sequitur within certain contexts. While it may be reason enough for those who don't care either way and just want to eat their meat regardless of any ethical implications to just say "that's what nature intended", none of that is going to be a valid argument for vegans who truly do care about delving deeply into the ethics of animal consumption. If we want our reasoning to be legitimate in the eyes of stalwart vegans (I personally don't care either way but I feel like I should participate in the conversion) then we must understand where they are coming from and what their reasoning for their belief is, and appeal to that. Whether or not I agree with someone's conclusion I'm still going to hear them out and see what makes them tick, as different people have different values and therefore approach ethical questions in a different manner with a different set of presuppositions.
I dislike the whole circle of life, appeal to tradition, naturalist thing for a couple of reasons. It might be sufficient for some, and that's great, I will encourage them to go hard on that, but in common parlance with vegans it doesn't come off as sound reasoning or appealing to an established objective standard. This sort of argument will only serve to push someone even further away from meat eating because it echos a sentiment of disinterest in the issue as hand and is entirely an arbitrary and subjective appeal to a value system that they fundamentally disagree with or that doesn't coincide with their own. Those vegans who use their brains more often than not (they exist!) know that our ancestors hunted for food, they know that humans are biologically omnivorous, they know that life feeds on live (this is necessary!) and they know that this is the way it has been for millions of years, and yet they are still vegans. It does not follow that because all of this is the case that we ought to continue to make it the case, it's a complete non sequitur. It also doesn't follow that because it is the "natural way", how we evolved, the will of evolution, etc, that such an action is absolved of any ethical wrongness simply by the virtue that it is "natural" or how it has always been. As Richard Dawkins says, evolution is a downright terrible place to get your morals. Nature is ruthless and unforgiving, and what it necessarily natural behavior is completely up for interpretation when we are speaking of human beings. We are programmed to survive and propagate our genes to the best of our ability, and this has spurred all sorts of atrocities in the past. Sometimes this even entails attacking an enemy tribe, eating the hearts of their warriors, and raping their women. But certainly nobody would agree that this is acceptable (except for ethical nihilists, amoralists, and the like. But these standpoints are incompatible with the "highly moralistic vegan save the world crowd" so I don't need to address them here). Humans are highly contemplative animals with superb gifts of foresight and reasoning, and thus we are able to partially subvert our intrinsic instructions by these very faculties to break free of our genetic tyranny (to the psychological determinists: because we are unable to do otherwise than what the aggregation of our psychological facticity dictates does not mean that we do not reason and moralize, we do. That's just so I don't have to clarify that later). I think that it is a good thing that I don't act with 100% compliance with what my replicator acts as though it wants of me. Clearly these brains of ours afford us the ability to question our own physiology and create our own meaning in this life, and whether or not one decides to do so or not, it is important to understand that the appeal to nature is not adequate from the perspective of those who have decided to forge their own meaning. The goals conscious humans, from the perspectives of their psychological selves is not the same as the goals that can be attributed to the goals of our genes (they act as though they have goals, even though they don't have minds per se). We want to live as happily with as great a quality of existence as possible, whereas the genes want us to propagate the genes to the greatest of their abilities. I think that I owe my consciousness enough to at least question why it is that I ought to do the things that seem so intuitive, that it what living the examined life entails.
We don't have to eat animals to be reasonably healthy (optimally healthy I will dispute) and we don't need animals to maintain agricultural land, and if we did it wouldn't follow that we would then necessarily be justified in consuming them before they have lived the entire span of their life. Maybe it used to be but there is new technology available that makes it not necessary to consume animals to live well. And so when faced with a genuine choice between one or the other, the vegan will tend to go with whichever entails the greatest potential quality of existence. There are happy happy feelings associated with being so kind and benevolent to animals and to thinking oneself more moral than those who choose to eat animals. There are also pangs of guilt (irrational, perhaps, but very much existing and very much relevant to them) accompanied with knowing that one was responsible for the death of an innocent animal. And it is these sorts of values that need to be appeal to if one wants to sway a vegan. Though I suspect that in the case of the threadstarter, it was more a matter of wanting to eat meat and simply needing re-encouragement that it is a fine thing to do and that it need not entail a blackened soul.
Vegans are people who think that animals are deserving of at least some ethical consideration. They believe themselves to be more virtuous if they extend empathy to animals and often this means that they reject consuming them at all, regardless of how they were raised and treated, as they value the lives of all sentient beings. A plant is not sentient, and anyone who has played with an adorable puppy dog and then tried to play with a cactus knows this. It is shooting oneself in the food to maintain that the life of a plant is the same as the life of an animal. There are differing degrees of consciousness, and while I think that the difference in consciousness of an animal and a human is great enough to warrant different treatment, I think that I personally ought to afford an animal some ethical consideration, whereas a plant needs none, as it is not a sentient mind that does not suffer in the same way. Pain is a mechanism by which we are alarted of danger and called to self-defensive action. A plant has no legs or claws and no way of extracting itself from a dangerous situation, and so there is no reason to believe that a plant feels pain in a relevant way. I think that sometimes we get confused with the difference between sentience and simply and a built-in positive/negative feedback mechanism (lean towards the light, manufacture the poison, etc) and so we attribute the characteristic of sentience to those that simply act like it sometimes upon the right . This reality works against vegans as well, in my eyes. The squirrels, mice (raccoons?!) that are killed by agriculture are a good point, but we humans are pretty smart and could probably use some sort of a fence to keep the little buggers out if we wanted to. There is a technological solution out there for anyone who wants to implement it. Whether or not we should care is another matter all together. I don't like the idea of making an animal suffer for extended periods of time, but I don't have a problem with killing it quickly and painlessly for food.
And so I reiterate that what functions as a perfectly sound argument against veganism for the individual does not always work to the benefit of that individual when attempt to sway a vegan from his or her beliefs.
Stabbing conventional wisdom in its face.
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