Surely all that's required is that it have a net positive effect?
Net positive taking into account all of the personal costs, yes. It's not enough that it merely reduces emissions, it needs to reduce emissions more effectively than other equally costly options. I get the sense that we're largely in agreement there though.
My original question was an attempt to ascertain whether the reduction in greenhouse gas emissions was truly your primary reason for choosing vegetarianism (with the choice made by weighing up the costs and benefits of various ways of reducing emissions) or whether it was a convenient 'added benefit' given a choice that was made partly or wholly for other reasons. The (seemingly) more common animal welfare justification for vegetarianism seems more directly linked to the particular decision to not eat meat than does a carbon emissions argument.
it needs to reduce emissions more effectively than other equally costly options.
Perhaps I'm misunderstanding, but this still seems inaccurate to me. If there is a more effective yet equally costly option O, but the total benefit of O+Vegetarian is still greater than the total cost of O+Vegetarian, then Vegetarian is still worth it (as is O). Your framing seems to deny this.
My original question was an attempt to ascertain whether the reduction in greenhouse gas emissions was truly your primary reason for choosing vegetarianism
Yes. It was, and is. I g...
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: