Or, if I become a vegetarian for reasons mostly related to animal suffering, I would want to judge others more harshly for not being vegetarians, which is very poor form in conventional social interactions.
Judging others is about making predictions on their future actions in morally challenging situations. If they eat meat, it's a good predictor that they will eat meat in future, but it doesn't say much about whether they'll jump into the canal to save a drowning child.
That's true as far as it goes, but it seems to me that jumping into a canal to rescue a drowning child is as morally easy as it gets: your explicit beliefs are nicely lining up with your intuitions and emotions.
Eating ethically is much harder; it involves the ability to make some sacrifices without the benefit of strong emotional spurs. Vegetarianism/veganism, assuming it's based on essentially consequentialist reasoning (not all of it is), is basically a real-world application of "shut up & multiply," which I find admirable.
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: