You're getting into dangerous philosophical territory here, which is not at all easy to resolve. If there are two animals with very similar brain states are they distinct animals? If not, have we doubled the subjective chance of an animal experiencing the state of the doubled animal? These aren't straightforward questions at all. See the Anthropic Trilemma.
I'm not sure how anyone could argue that bringing more suffering animals into the world is good. I support humane treatment of livestock, which I think makes for a net positive regardless of how the Anthropic Trilemma pans out:
If it turns out that most animals are so similar as to not count for distinct entities, but subjective probabilities still exist, so that increasing the percentage of animals in one state increases the chances of experiencing that state for an animal, then it is a good thing to raise lots of animals in a humane fashion.
If it turns out that animals aren't distinct and subjective probabilities can't be affected, then it seems the entire moral quandary disappears. The subjective experience of animals is forever fixed, regardless of our actions, so even factory farming wouldn't be unethical (although I would still support humane treatment of animals because I believe it makes for a healthier meal for me).
If it turns out that every animal is a unique entity, then the moral question must come down to individual cases. Should I bring this potential animal into existence? In this case I believe a close proxy for this question is: if this animal already exists, is it worse for it to have never existed? In the case of a humanely raised animal, I believe the answer is 'yes' to both of these questions.
I have noticed that among philosophers, vegetarianism of one form or another is quite common. In fact, I became a vegetarian (technically a pescetarian) myself partly out of respect for an undergraduate philosophy professor. I am interested in finding out if there is a similar disproportion in the Less Wrong community.
I didn't request that this go into Yvain's survey because I want more information than just what animal products you do or don't eat; I'd also like to see nuances of the reasons behind your diet. There are a lot more shades than carnivore/vegetarian/vegan - if you want to be a vegetarian but are allergic to soy and gluten, that's a compelling reason to diversify protein sources, for instance. I'd also like to hear about if you avoid any plant foods (if you think they're farmed in a way that's environmentally destructive or that hurts people or if you have warm fuzzy feelings for plants, maybe). Here are some questions that come to mind: