As a general rule I try to avoid foods made with additives or processes that originated from modern science, because I think overall the selection of cultural traditions over human history is more effective at eliminating non-obvious harmful practices.
I'm not strict about this, I only apply it to things I eat regularly. I don't try to convince anyone and I only mention it if it comes up. If I have children I'll feed them the same way and explain why, but I won't pressure them about it once they get old enough to procure their own food.
In most cases I have no opinion about other people's diets.
I dislike excessively cruel animal raising practices such as packing live chickens together so tightly that they can't move, but I'm not willing to devote my life to stopping it and anything less would have negligible effects in the absence of mainstream concern.
Even with the present, limited, state of knowledge about nutrition and health it seems to me that we can do significantly better than just avoid all additives or modern foods. I don't have much faith that traditional diets are optimized for long-term health. That said, I agree that this is not a bad heuristic to use on the margin.
Does your being honest have anything more than negligible effects on the amount of honesty in the world? It is not at all obvious to me that the marginal benefit of more vegetarianism is increasing in the number of people who shift towards it.
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: