Most people say that Buddhism 1 is not far away from vegetarianism. Is it true? In fact, most of Buddhists are not vegetarian. Buddhists must do Five Sila 2, but most of Buddhists did not and do not obey the First Sila: "do not kill". Eating meat is the cause of killing animals and it is clearly a violation of the First Sila.
Buddha Dharma 1 talks about dukkha 3 and how to overcome dukkha. So let us talk how to overcome dukkha. If we can control our heart and mind, then we can face the "challenge" of dukkha and get the "opportunity" of peace and happiness. But if we eat meat, there will be no self-control and there will be no peace and happiness at all.
A Buddhist should ease the dukkha not add the dukkha by killing animal or eating meat. Eating meat (the cause) and killing animal (the effect) will never be the teaching of true Buddha Dharma.
Buddhists want to save others from dukkha. This is the spirit of Boddhisatva. Boddhisatvas, however, must develop the heart of Metta or Maitri. Metta means Compassion or Mercy. Vegetarianism supports people to do Metta better.
"Save yourself first so then you can save others". This is the spirit of Arahat. Arahats, at least, should obey Five Sila to overcome dukkha. The First Sila, certainly, talks about vegetarianism.
Vegetarianism is surely the basic foundation to become Boddhisatva and Arahat in the same time. Because we do save ourselves from dukkha and we also save other living creatures from dukkha.
But some Buddhists often say, "Vegetarian? It's a funny idea. Cows are vegetarian, but cows never go to Nirvana 4. " But we are human not bovine. If we humiliate ourselves as carnivorous animal and do killing for living, actually we throw away the very precious opportunity to overcome dukkha. In fact, killing animal is avoidable dukkha and killing animal is against the spirit of Buddha Dharma that appreciates every life.
Buddhists believe that the next Buddha is Buddha Maitreya or Buddha Metteya 5. Some scholars say Maitreya will come several billion years later based on Buddhist scriptures. But some people believe He will come soon because, in fact, the technology do accelerate the years. Information Technology, for example, had broken down the national and traditional borders and it will ease Him to do His Great Work. One of His Great Work is spreading the teaching of vegetarianism. Now, through information technology, many religions and institutions adopt vegetarianism.
Maitreya or Metteya is a word derived from Maitri or Metta, so vegetarianism is absolutely the special character of Maitreya. Maitreya will always bless vegetarian people no matter what religions they have. That's why some people prefer to call Him as "Maitreya" rather than "Buddha Maitreya", because Maitreya belongs not only to Buddhists but also to every religious-vegetarian communities who wish peace and harmony in this earth.
Vegetarianism is surely the first step into the Holy Earth of Maitreya 6. People in the Holy Earth will do compassion and mercy towards animal and human. Human and animal will be one big community, live in peace and harmony. It is not an utopian world but a world of process. It depends on the process how to stop the killing of innocent ones.
It is our continuous struggle to make people realize that vegetarianism is a matter of human sanity as well as a matter of health and an ecological issue.

1. For more precise terminology, we will use Buddha Dharma instead of Buddhism. Western people translate "Dharma" as "ism". So Buddha Dharma is translated as Buddhism. But actually, Dharma is more than ism. Dharma means the TRUTH. BUDDHA DHARMA is the TRUTH of the whole MINDS, the whole HEARTS, the whole WORDS and the whole ACTIONS of BUDDHA.
2. Sila means Ethic or Rule. The Five Sila are 1] do not kill 2] do not steal 3] do not lie or cheat 4] do not do sexual affair or abuse 5] do not consume everything that can make you addicted (like alcohol, tobacco, opium, narcotic, etc). The purpose of Five Sila is preventing negative karma.
3. Dukkha means suffering, misery, pain, or something that cause sadness, discomfort or unhappiness. Buddha always spoke that life is dukkha because human tends to do negative karma. "Life is dukkha" is not a negative thinking but actually a real fact that we must face and solve with all of our sincere efforts.
4. Nir means no, vana means (negative) desire, Nirvana means extinguishing (negative) desire. And (negative) desire is the cause of dukkha, so we can say that Nirvana is another word of overcoming dukkha.
5. Buddha Siddharta Gautama Sakyamuni himself spoke about Maitreya as the Next Buddha. Maitreya is just like Messiah among Jews. Maitreya's movement was popular among Buddhists in India several centuries before Christ. In the same time, Messiah's movement was popular among Jews. Maybe the Silk Way is the only answer of this similarity.
6. Some Jews believe that in the arrival of Messiah, in the day when Heaven Kingdom is on Earth, people will be vegetarian. And the followers of Maitreya believe just the same. Some Jews are still hoping the arrival of Messiah. Some Buddhists are not only hoping the arrival of Maitreya but also preparing for it, spiritually and physically, through developing Buddhist-vegetarian families.