I'm a vegetarian, and I don't understand them either.
Here are my reasons for being a vegetarian:
  1. By cutting out meat from my diet completely, I feel I can eat anything else that strikes my fancy without worrying about calories, cholesterol, etc. I don't like worrying about the little details.
  2. Money-- meat is expensive.
  3. I'm not the tidiest person in the world, and if I accidently eat some veggies that have gone nasty, chances are I'll gag a little. Maybe suffer some indigestion. If I were to eat meat at an equivalent level of nastiness, I'd end up hospitalized.
  4. It makes logical sense to me that eating low on the food chain is more efficient.
  5. Half-jokingly: as the Earth becomes overcrowded due to us breeding like rabbits and ignoring the screamingly important task of settling nearby planets, sheer population pressure will force us all to become vegetarians. I'm a vegetarian because I like being just a little bit ahead of my time.

So, with all that being said, I still don't understand the shrill, self-righteous, Puritanical attitude so many vegetarians have. Some of them are in denial about our evolutionary heritage. Some of them like to mix it in with a fascist or luddite political agenda-- "we need to regulate everything in sight in order to protect the Earth from us evil humans". I'm embarassed to share a lifestyle with these people, and if anything ever makes me feel like sinking my pointy canines into a juicy slab of steak, it's hearing sermons from the Unabomber-wannabes of the world.

In closing, I'd like to officially go on record as urging everyone to eat cheeseburgers. Eat lard. Eat steel belted radials for all I care. I'd like for everyone to be healthy, but I'd like even more for everyone to make their own, independent choices.