I don't know what AlexU meant by "sanctimonious twits"... Like others on this thread, I have not encountered evangelical vegetarians. In fact, a lot of vegetarians don't want to talk about it, for fear of getting criticized.
But consider what Emily said
I admire the vegans: not sure that I could ever manage that! But nor do I see much of an ethical impulse to.
A lot of why people are vegetarians is to be admired for doing something difficult. It's important that they have some kind of reason as an excuse for doing it--they can't admit to showing off--but it's impressive and admirable to people who think that it is pointless.
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: