My intuition is that your view of animal happiness is closer to the truth than the vegetarians. First, I consider research on happiness even in humans, especially "Stumbling on Happiness" which book I highly recommend. Even for humans, happiness does not generally correlate with what you or I think would make you happy. A compelling example: conjoined twins are generally as happy as "singleton" (i.e. normal) people, but virtually no singleton would guess that intuitively. Generally, we adjust to the status quo across gigantically broad ranges: those who live in the slums of Bombay are not clearly happier or less happy than those of us living in mansions.
So I would imagine chickens in ooky coops, cows in stockyards, like humans, adjust to the mean. Then have their moments of pleasure and moments of pain primarily as variations around that.
And the terror or fear at slaughter? It seems very unlikely that they spend much time dreading it, as my dog trainer said to a couple who was sure the dog was punishing them for going out by pooping on the floor: "I think dogs live more in the moment than that." And I expect that for cows, pigs, and certainly chickens.
So far, we live in only one world of a possible MWI. So far, mammals are born, they live, they experience emotions positive and negative, and they die. How much sense does it make to adopt a moral system which thinks we are wrong for just doing what nature has very many animals do for millions of years?
So far, we live in only one world of a possible MWI.
I nominate this for the title of "Most Gratuitous Quantum Mechanics Reference of the Month".
(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.