Hey Marthman. Apologies in advance for the run-on sentences; they're not preventable. I've a BA in Philosophy, and was a vegan for 2 years during the pursuit of that degree. I did enjoy tremendously both the ascetic challenge and the health benefits of veganism, -- especially raw veganism and fruitarianism, both of which I tried for a few months during that period -- but was primarily a vegan due to moral concerns regarding the meat market; I was less against the concept of eating meat than I was with the concept of domesticated animals, and more specifically factory farming. During this time, I was taking a Moral Philosophy course with a professor that has authored multiple Ethics courses, and had a snobbish opinion about it being 'wrong' to lie to one's grandmother about her carrot cake being delicious, to which he responded, "We can't be completely moral -- are you a vegetarian?" to which I replied, "No, I've been a vegan for 6 months now. Are you not?" He stuttered so hard, and I felt so victorious. However; I am no longer of the belief that carnivore and philosopher are mutually exclusive titles.
I did not read your entire post, as it strayed from what I think is the error or in your ethical system or understanding: ethical egoism, and more specifically the concept of ethics as a privilege. Humans, and all animals, are completely selfish beings. Different people, and different animals at that, find different things to be to their benefit, and so they pursue those things. One of the most important things to particularly emotional people is the concept and sentiment of dignity or personhood, and this leads some to pursue seemingly altruistic activities and statuses as environmentalist, vegan, volunteer, and others. It's important to realize, however, that the only reason that this drive exists is for an elevation of one's own sentiment of dignity. Dignity allows one to believe they deserve justice in the world, rightful treatment from others, and to believe they are a part of a larger whole -- but all of this, in turn, is solely for one's own happiness. This is emotional selfishness.
Others, on the other hand, have a blunted experience of emotional need and desire. That is, they are more rational, or procedural, in nature. They still feel the loss of dignity, and its various manifestations. However, their procedures for success work at optimum efficiency when the prerequisite of dignity is not impinging upon their goals. However, these types of people will still attempt to attain and maintain dignified living if it is the most efficient means to their ends. This goes into a topic which is outside of the scope of the discussion -- the political philosophy of cultural technology and social engineering.
Bringing this back to the carnivore vs. omnivore dilemma: eating and purchasing animal products is simply more accessible, less costly, more pleasurable, and less difficult. Products like cheese and meat offer full meals at small, nutrient-dense portions.
The most important take-away from Philosophy, for me personally, is the concept of identity. Who are you? Do you identify with your body, or can you imagine waking up in someone else's, as you? Do you have disagreements with yourself sometimes -- about which course of action you should take? Which of the voices in your head are you? Are you any of them? Or are 'you' just a giant constitution under which many live, and whose happiness is under your responsibility? Figure that out, first, because when you realize what is truly happening, if you realize what is truly happening, you find that the most ethical person works tirelessly toward the goal of having lived a complete and fulfilling life, and reinforcing their identity. Your disgust toward non-ethical people is entirely understandable, but ultimately only so because if they are not ethical then they are not disposed to be of benefit to 'you'.
Suggested readings: Plato's Republic (who/what are you?), Aristotle's Ethics, Spinoza's Ethics, Nietzsche's On The Genealogy of Morals, Rand's The Virtue of Selfishness.