Since I became mostly vegetarian a few months ago, it's been pretty common for people to ask why. By that they usually mean something like "Out of the standard reasons for becoming vegetarian, which one motivated you?" For me, that question doesn't really make sense, since having many reasons for a decision is much better than just having one, and in fact I'm not sure that any single reason would have swayed me by itself. But since there are more reasons to be vegetarian than people think, I want to discuss them briefly here.
- Animal welfare
- I don't really mind the idea of animals dying, but the months or years of suffering that most farmed animals go through is pretty horrific. If I imagine what it is like to be a conscious being undergoing those conditions, that seems a particularly compelling reason to stop eating meat.
- I think the evidence is fairly clear that many forms of meat are bad for you, particularly processed meat and red meat, and particularly at the usual high levels of consumption. (Conversely, vitamin B12 is the only dietary requirement you can't get from a vegan diet, although it is found in dairy).
- Global warming
- Raising farm animals produces many times more emissions per calorie than plant-based food, and also leads to the destruction of forests on a massive scale.
- Infectious diseases
- The widespread overuse of antibiotics on farm animals is leading to the evolution of antibiotic-resistant diseases; it's only a matter of time before one develops which severely affects humans.
- Preventing food crises
- Producing meat requires much more land, feed, water and energy than equivalent amounts of plant-based foods. Producing less meat lessens vulnerability to sharp changes in any of those inputs.
- The justifications I used for eating meat are very similar to those which a slave owner might have used; I want to be morally better than that. Also, the attitudes of future generations towards carnivorism will probably be very similar to our current attitudes about slaveholding.
- Individual effects
- It might not feel like individually stopping has much impact. But if nobody eats meat, all meat production will shut down. If consumption decreases by 10%, then about 10% of production will shut down. If consumption decreases by one factory-farm's output, then on average one factory farm will shut down. If that takes 1000 people giving up meat, then it's probably reasonable to think you've each saved 1/1000 of the animals that would have been raised there, i.e. roughly however many animals you ate.
- None of the arguments against eating meat are knock-down proofs it's bad in all cases. If you spend a lot of effort making sure all your meat is ethically sourced (unfortunately, the free-range label isn't enough to ensure that), from farmers who don't use antibiotics, and raised in places which aren't viable for other crops; if you also avoid red meat and processed meat, and pay for carbon credits to offset environmental impact - then you're probably not doing any harm. But realistically, you're not going to do that. Fortunately it's less effort (and a better example to others) simply to become vegetarian.
- I'm currently cutting down on eggs, because the suffering that battery hens go through is comparable to the suffering of those raised for food. However, you don't need to do so in one swoop. A tactic my friends and I have been using is to stop eating any visible eggs, while ignoring those in cakes, etc. Similarly, halving your meat intake is about half as good as going entirely vegetarian (although it seems easier, motivationally, to stick to a clear line).
- Social pressure
- Most of my close friends are vegetarian, which helped me put pressure on myself and made it a question of when, not if, I'd become vegetarian. In fact, at one point a friend became impatient and bet me that I couldn't go vegetarian for 6 months. I wouldn't have taken the bet if I hadn't wanted to be vegetarian anyway, but since I did it was excellent motivation.
Update: Vegetarianism and veganism are great, but it's important to be aware that there may be much more impactful ways to help animals. I recently took part in a workshop where, amongst other things, we made very rough estimates of the value of donating to the Good Food Institute, a charity which funds attempts to create synthetic meat. Even using conservative numbers, it comes out shockingly high. Let's say ten million dollars donated now could speed up the end of factory farming by a month - a plausible estimate, since there's so little funding for research in this area right now, but also little reason to think we can't eventually create cheaper and better alternatives to farmed meat. There are perhaps 25 billion factory-farmed animals alive at any time, so this would save around 2 billion animal-years of suffering. So according to this estimate you could prevent 200 years of animal suffering per dollar. The point is not that this estimate is robust - it's largely speculative - but that whether you're vegetarian or not, there are probably very important things you could do to help animals very easily.