Ben writes via e-mail:
Sure thing, bro.
So first, no one seems to have a philosophical reason to eat meat. No one is taking a principled stand, thinking "Eating meat is the only way to save the planet, or the cows will fucking take over!" or waving signs that say, "GOD HATES PIGS" at PETA conferences. Meat eaters usually don't feel the need to justify themselves to vegetarians, since apparently a diet that includes meat is the natural state for humans: after all, our teeth are suited for both grinding plants and tearing flesh, and our digestive system has no problem dealing with a diet with lots of protein in it. Plus, we find it fucking delicious. How did that evolve unless meat is beneficial?
Of course, natural doesn't necessarily mean good; it's also our 'natural' state to live in caves and shit in holes. Indoor plumbing is both completely unnatural and totally fucking awesome. But it does seem to establish that eating meat is the default, and the burden of proof is on those who would have us act otherwise. They must provide compelling reasons why we should abandon meat. Maybe there are those reasons - why don't we poop outdoors anymore? Because it spreads disease and is generally unsanitary - but if there's no good reason to not eat meat, that's enough for meat eaters. The philosophical case for eating meat is simply the observation that bros love steak coupled with refutations of the arguments against bros loving steak.
It's important to keep in mind that "vegetarianism" is an umbrella term that covers a bunch of different diets - some vegetarians eat everything except meat; some don't eat meat or dairy; some don't eat meat, dairy, or eggs; some don't eat any animal products at all. Vegetarians have given a bunch of different reasons why we shouldn't eat meat, and there are a lot of subtleties. The most widespread and philosophical concerns, however, are grounded in animal rights.
So two key questions are: do animals have rights, and if so, do those rights forbid us from eating them?
Obviously we don't let dogs vote. Why? Well, one reason is that as much as bros love dogs, we know they're just not capable of understanding the political system. Dogs are loyal to bros, not ideologies. So they don't have a right to vote. But dogs definitely can feel pain, and so can cows, pigs, chicken, and just about any other source of meat. Peter Singer, a utilitarian thinker who teaches at Princeton, says that their pain is just as valid as ours - we're being speciesist (think 'racist', but with species) to ignore it. Humans have a special moral capacity, and as Uncle Ben taught us, with great power comes great responsibility. We have devised means of survival that don't entail killing animals, just like we've devised means of shelter that don't entail caves or outhouses. We're advanced enough that we don't need to eat meat, and we shouldn't kill animals needlessly.
Meat eaters respond to this in a couple ways - first, most of them reject that animal pleasure and pain really are as valid as human pleasure and pain. For starters, we have no way to measure it. Sure, cats yelp when you step on their tails, but how much pain is that compared to, say, a bro breaking a leg? How many fried ants add up to a beheaded chicken? Humans can communicate about pain and rank it. All we have are animal reactions, and they tend to freak the fuck out at the slightest provocation. Besides, even if we could measure animal pain, are we sure it is just as valid? Humans can anticipate, plan for, work toward, and remember distinctly pain and pleasure. Its why bros look good all the time - there's always potential pleasure to be had. Most animals just feel it and then... that's it. Sensation gone.
Animals bred for the specific purpose of being eaten present a special problem. If we breed a cow for the specific purpose of eating it, and it lives a comfortable and reasonably pleasurable life - enough pleasure to significantly outweigh the pain of a swift execution - and then its meat goes to create the pleasure of prime rib for some bros, doesn't that maximize pleasure way better that vegetarianism? Some vegetarians think it's wrong to create life with the express purpose of eventually killing it. Others question how painless a death we can really provide.
So a utilitarian says that animals do have a right not to have pain inflicted on them, and this might forbid us from eating them, depending on the subtleties of utilitarian theory and the treatment of animals. Of course, those are just utilitarian considerations. if you're not a utilitarian, they don't matter.
Maybe animals have other rights, but it's hard to see what those would be or on what basis they exist. Certainly not a social contract, since animals can't themselves reason morally or respect rights; tigers, for example, have historically ignored the right of magicians not to have their goddamn faces eaten off. Some philosophers reject the idea of animal rights or obligations of humans to animals out of hand. If an animal can't reason, can't respect rights, can't articulate rights, can't exercise rights, then how the hell can it have rights? What does it mean to have rights you can't exercise at all, even in principle? Do I have a right to collect rocks from Mars? It's hard to say.
Maybe, even if they don't have rights, we just shouldn't be cruel to them. Kicking puppies seems wrong, doesn't it? Some vegetarians think that intuition points to something deeper, and it's just plain wrong to kill animals needlessly. Most meat eaters just aren't satisfied with this claim, and have different intuitions - animals eat other animals all the time, even when they don't need to. Grizzly bears work real hard for fresh fish, even though they could get by on roots and carcasses, and that doesn't seem wrong at all. In fact, it's kind of cool to watch. Bears are majestic fucking creatures.
It boils down to this: most vegetarians have moral reasons that compel them to abstain from meat. Meat eaters either don't find those reasons compelling enough, or they find ways to meet them without completely avoiding meat: if the concern is animal pain or cruelty, maybe we can just treat them better while they're alive, problem solved. Or maybe abstaining from meat altogether is the only moral choice.
You can find a debate on animal rights between Judge Richard Posner and Peter Singer online here.
Peter Singer's Animal Liberation lays out the case for consideration of animal pain and pleasure.
Jean Kazez's Animalkind: What We Owe to Animals (Blackwell Public Philosophy Series) is a good survey of the literature on animal rights broadly.