Environmental and efficiency concerns are my main motivation, particularly GHG emissions.
Would it be accurate to say that your primary concern is that there are negative externalities involved in meat production that are not reflected in the price of meat products? If the largest negative externality that concerns you is GHG emissions do you feel that your reasons for not eating meat would be eliminated if the negative externalities were priced in through some kind of energy tax or cap and trade system? Did you ever consider eating meat and purchasing carbon offsets to make up for the unpaid negative externality? It sounds like you don't miss meat much any more but you say that you used to enjoy it so presumably there would have been some additional price you would have been willing to pay in the form of a carbon offset or perhaps a charitable donation of some kind?
Question: Given current regulatory regimes, how effective is buying carbon offsets? My impression is "not particularly."
Furthermore, eating a more vegetarian diet does not compete with buying offsets. One could do both. In fact, because vegetarian food is often cheaper (and would be relatively cheaper still if wasteful agricultural subsidies were eliminated), eating more vegetarian leaves people more money for good causes.
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: