In case you don't know what a vegan is let me give you the gastronomic hierarchy and where vegans fit into it.
Omnivores are looked down on by
Those who don't eat pork, who are looked down on by
Those who eat only chicken and fish, who are looked down on by
Those who eat only fish, who are looked down on by
Vegetarians, who are looked down by
Vegans (we don't eat eggs, dairy, honey, or any other animal related product) who are looked down on by
Raw food vegans (they are the creme of the disciplined)
Vegans are pretty high on the "food chain" when it comes to lifestyle eaters. My own personal vegan philosophy has evolved in its current incarnation. The core ideology remains the same however.
Health For whatever reason vegan eating really agrees with me. I seem to have no problems maintaining my diet in a world of unhealthy and animal product ridden food. It just works for me. It allows me to avoid 99 percent of the junk I would normally pollute my body with. When I wasn't a vegan I had a very hard time controlling my weight. I also had high blood sugar, high blood pressure, and high cholesterol. I now suffer from none of those things.
Environment There are many blogs and web sites more articulate on the ramifications that the animal product industry leave on the environment. Here is a great article on vegan.com
http://www.vegansociety.com/html/environment/AnimalsThe cruelty of the meat production industry in this culture is not to be believed. There are numerous books and sites devoted to this. Here is a good essay.
http://www.goveg.com/vegkit/meet.aspSo there you have my trinity that keeps me on the vegan path. If any one of the components isn't there for me, the other two always step in. Feel free to have a chat with me anytime about it. Conversations on the subject can be in depth and fascinating.