Veganism is the belief that one should not eat any animal products. Many vegans are so because of dietary reasons, although not as many people are vegans for health reasons as there are health vegetarians. A large principle for most vegans is a respect for all life on Earth, not just human life. With the current treatment of animals and humans on big company farms, many vegans believe that it is irresponsible to support that. Even on small "mom and pop" farms who try to be kind to their animals, the simple fact remains that in order to make any kind of profit the animals must be exploited. Previous health concerns have mostly been negated, such as the lack of vitamin B12 in vegan diets. Vitimin B12 comes from a bacteria found on both plants and dead animals, but is generally washed away on plants. So, consuming a B12 supplement does not necessitate eating animal products. Veganism has been criticized for a multitude of reasons, but generally if someone has a problem with them it is either out of fear of change or because of a lack of understanding.
After learning more about Pacifism, Gary decided that he could not in good conscience use animal products, he had to become Vegan and that's how he got started on Veganism.