In Theravada, vegetarianism isn't a requirement. The Buddha himself rejected Devadatta's demand to institute vegetarianism as a requirement. Moreover, he never said that simply eating meat in and of itself is unwholesome (akusala). However, the underlying question that I think is being so hotly being debated here is, Does that mean that purchasing meat is the same as purchasing produce? My answer is no.
Essentially, the meat that one purchases from the grocery store must come from an animal that's been deliberately killed by someone. whereas the same cannot be said about the fruits and vegetables that one purchases from the grocery store. Fruits and vegetables aren't sentient beings, and harvesting them doesn't automatically entail the intentional killing of any sentient beings. If any sentient beings are killed in the harvesting of a fruit or vegetable, it's conceivable that it was accidental rather than deliberate.
In the case of meat, that's not the case. The animal must almost always be deliberately killed by someone. It's true that purchasing meat from the grocery store does n't ential the kamma of killing for the purchaser; however, a well-informed practitioner should be aware that an animal has to be deliberately killed at some point for that meat to be available. Abstaining from eating meat doesn't free one from the web of killing and death, but it's hard to argue against the fact that doing so would at least help by not directly contributing to the meat industry that's built around the raising and killing of animals specifically for their flesh.
The way I see it, no source of food is 100% free from harming sentient beings, but the consumer does have the power to limit the amount of harm done. This can be achieved in many ways, e.g., not buying meat or at least buying meat from farmers and companies who treat their animals more humanely, buying eggs from farmers and companies who allow their hens to roam freely, buying produce from farmers and companies who don't use any pesticides, etc. So the consumer isn't entirely powerless. They can have an effect on how many animals are killed, the manner of their deaths, and/or how they're treated in general, as well as the amount of pesticide-free produce that are sold, etc.
When going to the super market, for example, that particular store most likely keeps a record of all purchases and uses that information towards influencing store policy. Theoretically, if the the majority of consumers cease buying meat, the demand for meat will go down and less animals will need to be killed in order to meet the demand. In addition, if the majority of consumers who do purchase meat and dairy products purchase them from farmers and companies who treat and kill the animals in a more humane fashion, other companies will naturally follow suit due to the potential profit of such business practices. The same holds true for the kind of produce we buy. In a capitalist society, money is the greatest impetus for change pure and simple.
All of this ties into to the idea of personal responsibility and how far we, as individuals, wish to be socially active in regard to our Buddhist beliefs and practices. It's a personal choice that we each must make. For some, purchasing meat is perfectly acceptable to them since they know that the animal has been killed by another person. But for others, the purchasing of meat might not seem so acceptable when they consider things such as what meat is and how it gets to the store.
Therefore, while I completely agree that in regard to the first precept the Buddha taught about personal responsibility in the form of regulating our own actions of body, speech, and mind, that doesn't mean that we should simply turn a blind eye to where our food comes from. Doesn't that also fall within the realm of personal responsibility? Hence, while I agree that vegetarianism isn't a requirement, I do think that it's at least a compassionate option for Buddhists to adopt. That's why even though there's nothing in Theravada that states this lifestyle choice is necessary or even preferred, I generally try to avoid buying meat or anything with meat in it when I go to the grocery store, out to eat at a restaurant, etc.
Just to be clear, however, I am not trying to demonize meat eating or the meat industry because that's a pointless crusade. As I said, abstaining from eating meat doesn't free one from the web of killing and death. Killing and death are awful facts of samsara that have the potential to arise because there are sentient beings whose minds are defiled by greed, hatred, and delusion. Besides removing oneself from the cycle of birth and death altogether, there are worldly solutions to these problems, but these solutions can merely limit the potential harm to other sentient beings at best.
In essence, besides escaping samsara, there are no perfect solutions. On top of that, condemning or demonizing another for their complicity means that we should also condemn and demonize ourselves as well. If we want to, we can find reasons to demonize internet usage. I doubt that most people are aware of how many birds are killed each year by microwave towers, but one could reason that every person who surfs the web or sends out an e-mail contributes to those deaths. Shall we cease to use the internet then?
My point is that choosing to be more socially active in our respective practices is an admirable thing to do. Nevertheless, we should never forget the very nature of samsara. In his introduction to The Four Nutriments of Life: An Anthology of Buddhist Texts, Nyanaponika Thera echoes:
- If we wish to eat and live, we have to kill or tacitly accept that others do the killing for us. When speaking of the latter, we do not refer merely to the butcher or the fisherman. Also for the strict vegetarian's sake, living beings have to die under the farmer's plowshare, and his lettuce and other vegetables have to be kept free of snails and other "pests," at the expense of these living beings who, like ourselves, are in search of food. A growing population's need for more arable land deprives animals of their living space and, in the course of history, has eliminated many a species. It is a world of killing in which we live and have a part. We should face this horrible fact and remain aware of it in our Reflection on Edible Food. It will stir us to effort for getting out of this murderous world by the ending of craving for the four nutriments.
I don't think my vegetarianism makes me a better Buddhist than others, but I do find that it lightens my mind whenever I reflect on the fact that I strive to practice ahimsa (harmelessness) as broadly as possible.