I was vegetarian when I discovered Buddhism in May. Like many I interpreted "Non killing" as being straightforward, and including the idea that eating meat was contributing to killing.
Then I read this thread and in November became an omnivore again. Of course I also received transmission from ChNN. Interestingly, while I knew about the karmic link practice, I didn't know about the mindfulness of the animal sustaining me and thereby generating merit for helping give life to a Dharma practitioner, but I have been including that in my mindfulness as well just because it made logical sense.
Those who think that a Tibetan Buddhist who eats meat somehow revels in the death of an animal are wrong. Those who think that just because meat is involved there is some "gruesome appetite" being fulfilled are also wrong. This would be like saying anyone who has sex is fulfilling some twisted fetish, or anyone who enjoys working out has an obsession with their body image.
Personally when I eat meat I fully contemplate its conditions, its suffering, the life it probably lived, its death. I actually meditate on the flesh itself, attempting to merge my mind with its essence and thereby get an idea of the sufferings that being actually felt, to see the world from its eyes, to understand what it was like to live like it lived, up to the moment of its death. I even go so far as to think about the part of the animal involved, how the animal was slain and then has this piece of its flesh lopped off, processed in this or that way. Sometimes the contemplation brings me to tears. Then with the aforementioned mindfulness I take my first bite of meat. So anyone who thinks that there is this total lack of compassion in such a practice, that one is just some disgusting gluttonous monster reveling in consuming flesh and blood is wrong, at least as a generalized sweeping statement. There are people like that, but they are never Buddhists. They are the ones who are proud to be carnivores, who have no thought for the fact that life that doesn't think is also sentient and also wants happiness. They hunt, and enjoy killing less fortunate beings. They smash bugs with zeal, and they think anyone who looks upon non human life as worthy of compassion are just nutty tree hugging hippies, weaklings who aren't "Man enough" or whatever.
Now of course I paint this compassionate picture of myself, but the truth is that while I strive to do this whenever I eat meat, and I strive to be mindful of many different things whenever I eat at all, sometimes I don't. Sometimes I am just hungry and distracted, and start eating whatever is in front of me without any mindfulness. I usually realize within a few bites and correct myself. But I am just saying that sure, selfishness can be involved in this as well as anything. Its hard to be mindful 24-7. When we eat vegetarian, we are equally in the wrong if we do not consider the food we eat as being causes for different kinds of suffering. In fact we should always be mindful of our food, from where it comes, the process involved, the suffering involved.
Think about it like this. Non local, non organic food has many harmful elements. Pesticides for example are used with the specific intention to kill. Now, in terms of the AMOUNT of beings killed, pesticides kill far more. Hundreds of thousands in a single sweep? Who knows. Not to mention whole areas of land are cleared in order to make room for crops, in south america the rainforest is clearcut in order to plant things that are shipped around the world. When you look at vegetarian food, a lot of it, if its not local and organic, destroys countless lifeforms, and much of it is done with the intention to kill. Then there is the toll on mother nature. The shipping, the trucks being driven, the packaging and so forth. So whatever we do, we can't avoid contributing to countless deaths. Its not just some fancy way of excusing eating meat, its true. Pesticides are used with the intention to kill, the action is fully carried out.
Furthermore what the teachings state is that all composite entities are bound to become food for other composite entities. There is no way to escape this fact. Composite entities (Which includes everything we see, even the sun) are only sustained by consuming something. If you were to kill some animals and even humans, throw them in the ground, put dirt on them and wait for them to decompose, that soil would become rich with nutrients. Plant some plants there, and the plants will consume it. So even plants ultimately can be considered meat eaters in this respect. Its a cycle of life and death, which are not different but actually just different stages of the same thing, like youth and old age, or seed and fruit. Finally if there is any chance that my eating meat will be a cause for a being to hear the Dharma teachings and to increase its merit, then I will do it despite my wish that there was no killing of animals at all.
I understand the argument of contribution, if you eat meat, you contribute to there being a meat industry. Yet the basis of this argument is flawed. To say that if everyone "stopped eating meat" there would be no industry can be applied to anything wrong with our samsaric world. It would be like saying "If only everyone would practice Dharma with good intentions, the world would become enlightened" and then being upset at someone specifically for not practicing Dharma, and blaming them as being the cause of the sorrows of this world. Or it would be like saying "If only everyone would give to others, there would be no poverty" except that will not happen, peoples delusions won't allow that kind of generosity on a scale to make an impact. So you can give to others and think "That person over there is not giving generously, they are the reason there are poor people in the world". In the end though, all of these arguments come down to a single essential point.
The reason there is any suffering at all is because of ignorance. So, whatever you seek to accomplish in terms of removing a defect of our samsaric existence, seek to remove peoples ignorance. If everyone stopped being ignorant, then all these problems would stop existing.