What strikes me as particularly weird is that I have a vegan friend who made a point of saying "I'm not going to tell someone else they shouldn't eat meat." I don't actually know what she meant by that - whether she honestly didn't think it was her business, or whether she simply had observed that telling people they shouldn't eat meat has the opposite intended effect - they get pissed at you for telling them what they should and shouldn't do, and either ignore you or eat more meat just to spite you.
If she meant the latter, I agree. I don't think I've ever gotten someone else to become Vegetarian, but the approach that seems to produce most.... "respect" I guess is when I:
a) Make an effort to point out that I will have a hard time eating at a particular restaurant or event because of few vegetarian options. I say this as matter-of-fact-ly as I can. When people go "wait what?" I say "yeah I'm vegetarian" without attaching any particular judgment to it.
b) when/if people ask "why," I focus almost entirely on reasons to cut back on meat that are [i]entirely in humanity's best interest.[/i] Most people are vaguely aware that there are "health reasons". And in fact, a lot of people say with hopeful looks "for health reasons, right?" because I don't sound judgy, and they have assumptions that the health-vegetarians are cool whereas the ethical-vegetarians are judgmental jerks. What people DON'T usually realize how bad the meat industry is for humanity as a whole (by way of the environment).
c) when I get to the ethical concerns, I focus specifically on factory farming. I'm not 100% sure how I feel about the absolute moral weight of animals who are killed humanely for food, but letting people feel like there's SOME way to ethically eat meat makes it feel less like I'm attacking them (even if that ethical way will almost never be relevant to the food that they'll have access to).
People SHOULDN'T need more reason than "animals are raised in cages, given growth hormones to the point where they can barely walk, left to sit in their own feces and then killed." But the magnitude of that reason is such that most people can't process it. So it's pretty convenient that there's plenty of other good reasons to help open people up to the idea.
but letting people feel like there's SOME way to ethically eat meat makes it feel less like I'm attacking them
This is called leaving a line of retreat, and it's a very good strategic consideration within a disagreement.
(Note: I wasn't quite sure whether this warranted a high level post or just a discussion. I haven't made a high level post yet, and wasn't entirely sure what the requirements are. For now I made it a discussion, but I'd like some feedback on that)
I've been somewhat surprised by the lack of many threads on Less Wrong dealing with vegetarianism, either for or against. Is there some near-universally accepted-but-unspoken philosophy here, or is it just not something people think of much? I was particularly taken aback by the Newtonmas invitation not even mentioning a vegetarian option. If a bunch of hyper-rationalists aren't even thinking about it, then either something is pretty wrong with my thinking or theirs.
I'm not going to go through all the arguments in detail here, but I'll list the basic ideas. If you've read "Diet for a Small Planet" or are otherwise aware of the specifics, and have counterarguments, feel free to object. If you haven't, I consider reading it (or something similar) a prerequisite for making a decision about whether you eat meat, just as reading the sequences is important to have meaningful discussion on this site.
The issues:
1. "It's cruel to animals." Factory farming is cruel on a massive scale, beyond what we find in nature. Even if animal suffering has only 1% the weight of a humans, there's enough multiplying going on that you can't just ignore it. I haven't precisely clarified my ethics in a way that avoids the Repugnant Conclusion (I've been vaguely describing myself as a "Preference Utilitarian" but I confess that I haven't fully explored the ramifications of it), but it seems to me that if you're not okay with breeding a subservient, less intelligent species of humans for slave labor and consumption, you shouldn't be okay with how we treat animals. I don't think intelligence gives humans any additional intrinsic value, and I don't think most humans use their intelligence to contribute to the universe on a scale meaningful enough to make a binary distinction between the instrumental value of the average human vs the average cow.
2. "It's bad for humans." The scale on which we eat meat is demonstrably unhealthy, wasteful and recent (arising in Western culture in the last hundred years). The way Westerners eat in general is unhealthy and meat is just a part of that, but it's a significant factor.
3. "It's bad for the environment (which is bad for both human and non-human animals)." Massive amounts of cows require massive amounts of grain, which require unsustainable agriculture which damages the soil. The cows themselves are a major pollution. (Edit: removed an attention grabbing fact that may or may not have been strictly true but I'm not currently prepared to defend)
Now, there are some legitimate counterarguments against strict vegetarianism. It's not necessary to be a pure vegetarian for health or environmental reasons. I do not object to free range farms that provide their animals with a decent life and painless death. I am fine with hunting. (In fact, until a super-AI somehow rewrites the rules of the ecosystem, hunting certain animals is necessary since humans have eliminated the natural predators). On top of all that, animal cruelty is only one of a million problems facing the world, factoring farming is only one of its causes, and dealing with it takes effort. You could be spending that effort dealing with one of the other 999,999 kinds of injustice that the world faces. And if that is your choice, after having given serious consideration to the issue, I understand.
I actually eat meat approximately once a month, for each of the above reasons. Western Society makes it difficult to live perfectly, and once-a-month turns out to be approximately how often I fail to live up to my ideals. My end goal for food consumption is to derive my meat, eggs and dairy products from ethical sources, after which I'll consider it "good enough" (i.e. diminishing returns of effort vs improving-the-world) and move on to another area of self improvement.