I have been a vegetarian on and off for about 2.5 years now. During this time I never stopped questioning the moral and logical foundations of that choice of mine and I have found that being able to explain well enough the reasons or social effects of being a vegetarian is not easy. Below, I discuss, in a fairly relaxed and non prioritized manner some of the core concepts and issues of vegetarianism.

1. Moral basis: obviously, if we are to accept that the feeling of empathy is naturally occurring (i.e. is inter-social), we need to acknowledge that its existential (in the Sartrian sense) nature can potentially permeate classes other than the human. In fact, from an empirical perspective we can clearly see that it does. However it can also be clearly seen that this feeling of empathy can get easily misguided, e.g. ridiculous empathy feelings toward anthropomorphic or animal like toys. Fortunately, philosophy, logic and science do come to the rescue: to help guide and focus our sense of empathy we need to first decide what the property or properties that rouse our empathetical feeling toward objects are. It seems that the single most important such property or rather state is that of suffering. Empathy can be felt for anything that exhibits certain side effects of suffering, e.g. certain facial expressions, or movements of distress. However to protect ourselves from being fooled by appearances that do not necessarily go any deeper we need to dig for the essence of suffering. See below.
2. The Essence of Suffering: philosophy and common sense seem to predominantly converge to the conclusion that suffering and self-consciousness are closely related; specifically, that self-consciousness is a prerequisite for any kind of suffering (as we humans know it, understand it and define it) to be experienced. If the argument for suffering is reduced to a level of granting suffering potentiality to anything with a nervous system then we will have to deal with such absurd paradoxes as that of the suffering freshly cut-off octopus leg that is dumped into boiling water or the seemingly obvious (to anyone who has had a operation at least) fallacy that persons who have an operation suffer during the process, when in fact they have no memory of any suffering, post-surgery. So, it seems that all kinds of suffering that we humans have experienced (and we therefore project to the objects that receive our empathy) are of the conscious kind. Take away consciousness and immediately suffering loses, at least in my opinion, its essence.
3. Consciousness and the Brain: Contemporary neurological evidence and research seem to agree that the part of the brain where the miracle of consciousness occurs is the neocortex. This is where the brain entities by the name of "psychons" occur - the recursiveness of their very nature is a witness to their purported functionality which allegedly occurs at the quantum level: making the brain conscious of itself (e.g. see here: Evolution of Consciousness). The thing is that all fish and reptiles (as well as evolutionarily more primitive lifeforms) completely lack this part of the brain (not even a hint). On the other hand all mammals (even the most primitive rodents) have a neocortex (with its size and complexity varying significantly) which means that one one has to grant them some level of self-consciousness (which, in my opinion, it is irrelevant, from a moral perspective, how primitive it is as long as it exists). Birds do not have a neocortex per se but they have a different, not existent in mammals, brain part that allegedly also gives rise to some form of self-consciousness. What this means is that, at least based on what we know or think we know today (which is all we have really if we do not want to enter the degrading path of religious faith), not eating fish or other non-mammal and non-avian animals does not make sense if you do it in order to prevent their suffering.
4. Humanitarian Killing of Animals: or rather "Morally acceptable killing of animals that allegedly exhibit some form of level of consciousness"- just to make things more explicit as well as conceptually sound. Is it a solution? Let's first make explicit the conditions under which I think such a statement does not become an oxymoron. Both the suffering of the animal itself and the suffering of its social circle would have to be ruled out. Just killing the animal in a way that is very fast and allegedly painless will not cut it simply because the process that leads to the killing is not yet refined enough not to generate some form of pre-death agony or at least feeling of approaching grave danger. Then there is the possible social suffering (however primitive) of the other animals that will miss their friend or kin or will even hear its dying groan. The only possibility of this happening in a way that is possibly morally acceptable is by raising groups of animals in complete separation and then killing all animals in the same group at the same instance, instantaneously. Very difficult but maybe possible.
5. Humanitarian Killing of Humans: In the previous point something sounds wrong however; following the thread of our argument up to now, we would have to extend it into human territory. Why, then, would it be wrong for someone to do the same (i.e. kill in a humane way) with whole groups of people? Imagine a hypothetical still undiscovered little tribe in the middle of the Amazon. They are all happy, having their yearly fest, dancing around a nice bonfire, eating anaconda stew and having group sex - a huge orbit based particle gun focuses and zap: disintegrates all of them, at the same time, in less than a nanosecond. They never suffered. None will miss them or suffer by their loss as none outside the tribe knows them. Why does it feel wrong? Lack of motive is not the reason as we can also hypothesize on a motive like the zap gun being controlled by some religious cult that believes in humanitarian zapping of sinners and it just so happens that the stew is really human stew; it would still feel wrong. Beyond the socially and legislatively conditioned truth of murder not being defined on the basis of suffering of the victim or others, I reckon the reason is the same that makes us dread death. Death is not only about pre-death suffering and the mental-existential-conceptual terror of non-existence. It is also about the ultimate form of loss of control and a testament to the futility of our aspiration of ever having real control over anything non-conventionally formed, including our very selves. The possibly completely theoretical possibility of taking somebody's life with zero suffering of him/her or anyone else presents us with a moral problem that could be as important as it is unsolvable without the introduction of faith in some kind of metaphysical system.
6. A meat-eating society with a meat-eating history and evolutionary past: Those who purport vegetarianism as the only acceptable/desirable dietary orientation for humans sometimes commit the error of oversimplification of the issue. To add some commonly overlooked issues that they may want to consider:
   • It is considered a fact (by the majority of athropologists) that we owe our very survival (as a species) to this point in time to our meat eating history.
   • It is a medical fact that our systems are evolved to consume meat better than vegetables.
   • It is a fact that a significant percentage of people will develop a number of medical conditions (some serious, some not as much) if they become vegetarians or vegans
   • There is a fundamental contradiction in claiming to be a vegetarian while living in a predominantly meat-consuming society, simply because diet is only part of a modern society's practices that consume animals in countless indirect ways.
   • The usual excuse that for something to change some people ought to start changing certain practices on their own before their practice becomes mainstream, although logical, may actually be misplaced as the prerequisite of strong motivation for mass change may be missing, e.g. many people will not accept that animals like pigs and cows are conscious enough to deserve empathy, major religions like Christianism and Islam support and even promote meat consumption. Further, if this claim of people practicing vegeterianism was true then we would have seen some kind of results by now; in fact, quite the opposite is happening: Globally, the demand for meat has never been greater, and is predicted to rise by a further 50% by the year 2020, spelling death and misery for billions of farm animals. Increasing (poor) human populations will put added pressure on wild animal populations, and the development of genetic engineering and xenotransplantation (the transplanting of vital organs from animals into humans) will further erode the status of animals. In my opinion, vegetarianism will not catch on until problems like that of global poverty and the social class gap in capitalist societies are addressed.
   • Eating cheap processed meat products makes economic sense for low class people that in fact seem to be growing more and more (e.g. in Brazil you can eat a burger for 30 eurocents, an amount that cannot buy you a coconut in the same country). As long as low income problems in societies are not addressed the lower classes will not even think of becoming vegetarians; this is simply a pactice dictated by the need to survive in a society that due to its meat eating tradition (that was not seriously questioned on a moral basis even 50 years ago) has perfected and in fact directed its food infrastructure towards meat production, processing, storage and selling.
7. Social marginalization of vegetarians and vegans: does it help them achieve role model status?
   What I am basically referring to here is this unnecessary and in fact hypocritical polarization that is created by the vegetarians explicitly or implicitly claiming that non-consumption of animal products somehow means their exemption from the moral responsibility for the killing of countless possibly suffering animals, while, in fact, their very being part of the same society and relying on its other blood-bathed goods and services usually manufactured and provided by ignorant meat-eating peasants makes them no different at all especially since it is probably only their coincidental birth and upbringing in a higher social class that provided them with the related information and further the possibility of becoming vegetarians. A healthier approach would be to preach vegetarianism, to practice it as much as possible but to also share blood with their fellow comrades of all social classes in a recognition of this human society's history and social pragmatics. I really think this practice would have had better results.
8. Vegetarian related up-tightness causes suffering to themselves and others, especially those close to them.
   This is related to the previous point. The moral breakthrough that vegeterians think they achieve comes at a price. They need to either stay within the tight confines of vegetarian societies and circles or consistently fight their flesh coveting while friends and relatives stuff themselves full of the stuff. This can certainly make them irritable and in fact paranoid (there certainly seems to be a connection between malnutrition and paranoia) that can often be the reason of a certain negativity being injected into their environment. They are also known to make a fuss over what exactly their order contains while in restaurants that ignore vegetarians in their menus.
9. Motivations: helping animals, relieving your conscience, feeling superior, satisfying your family or peers...
   Obviously, motivations behind being or becoming a vegetarian are not necessarily related to helping the animals (like being baptised a Christian does mean that you do it because you really believe in Jesus' teachings). One can be a vegetarian because of religious reasons, because his family also is, because the girl he likes is or because he wants to somehow show everybody how much better than them he/she is.
10. Gas: this varies from individual to individual but a good reminder of how you are not meant to only eat vegetables is the amount of gas you will be producing (and I don't know if this gas could contribute to global warming - someone should do phd on this) if you do. There are a number of cases where a completely vegetarian diet has, due to some DNA based intolerance, produced horrifying results in this respect.

Conclusion
I really believe tha there is a strong possibility that mammals do in fact suffer when being used for food production. Therefore, I do believe that the removal of red meat from one's diet (if medically alowable) is something morally desirable. However, I believe that one should not be a strict vegetarian or red-meat eating abolitionist (i.e. frequent exceptions should be allowed) given the current social pragmatics; this is because I really think that those who agree that eating red meat is something that should stop have a better chance to actually make it stop by doing the following:

1. Working towards alleviating world poverty and social class related injustice in western societies
2. Preaching red-meat avoidance, practicing it to a good extend and educating people about it all.
3. Not allowing themselves to be perceived or even become the "others" in the eyes of those who do not know what and why when it comes to red meat consumption. This can accomplished by sharing blood with them.

Technorati : death, morality, vegeterianism