I've been committed to vegetarianism most of my life. When people ask why, my reply is usually, "whatever reason you can think of." There are moral, ethical, religious and, probably most important for alot of people, health reasons, for eliminating animal food from the diet. Here's a look at them from my perspective:
1. The Ethical Reaons: Killing, even of an animal, in self-defense, is at times necessary for our survival, but rarely. Killing, even of an animal, for reasons other than self-defense, is for pleasure or self-gratification (with the possible exception of taking an animal in a survival situation, which I admit that I would do if necessary). But it is not generally necessary for our survival on a daily basis, and hunting and fishing are blood sports (see pleasure and self-gratification).
So you don't kill it yourself, but buy it wrapped in plastic in the supermarket. Haven't you paid someone else to do your dirty work for you?
And consider the plight of livestock: Let's face it, factory farming is not the most compassionate industry. In fact, there is no animal industry that does not entail some element of cruelty, be it animals for food, racing, medicine, or fur. Even the pet trade is not immune; so choose your pets and their breeders wisely. I also advocate adopting shelter or rescue pets, but I digress. I won't bore you any further with it here, because there are multitudes of websites and publications that address these issues far better and in greater detail than I can here.
2. Spiritual Reasons: Other than some Buddhist and Hindu sects and the Seventh-Day Adventists, there are few religious groups that advocate non-meat diets.
Early on I found it difficult to love some animals and eat others. I was being compassionate to dogs and cats and horses, but not pigs, cattle and sealife. Once as a young girl I attended a service at a Catholic church where they were celebrating the feast day of St. Francis. I thought it both odd and beautiful to bring animals to church.
One of the best books I have ever read on the religious aspect of vegetarianism is Judaism and Vegetarianism, by Richard H. Schwartz, Ph.D. (Micah Publications). From Genesis 1:29 to the laws of kasher and beyond, Dr. Schwartz gives Biblical insights and explores Jewish tradition to justify a non-meat diet.
3. The Health Reasons: There are many nutritionists and doctors who have expounded on how unhealthy animal food is for us. When people suffer from hypertension or arteriosclerosis, most doctors tell them to refrain from salt. But salt is not the culprit: the animal food that cause the plaque and lack of elasticity in the arteries is. But few in the medical profession recommend deletion of animal food from the diet.
Now, don't believe that just becoming a vegetarian, in and of itself, will make you healthier. I know a quite a few vegetarians who, for ethical reasons, don't eat meat or animal products, but otherwise don't watch what they eat. But even though sodas and potato chips aren't animal food, inordinate amounts aren't good for you. I know many meat eaters who are healthier than these over-weight sugar addicts. A junk food junkie of any stripe is tempting fate.
4. Economic reasons: It takes a greater amount of resources to grow animal food that plant food. In fact, animal food is indirect protein: plants must be grown to feed animals that could be used to feed people. Let's face it, we can't feed the world on hamburger: it's unsustainable. Most of the world is fed on beans and grains.
And on a personal level, it's far less expensive.
We can find support in any of these reasons, in any order. In fact, in my own life, they have changed order. Originally, I became a veg when I was young, in school, and needing to save money. Eliminating meat from my diet eliminated a great expense. I then embraced the spiritual and ethical reasons, and finally, realized that my health was better than most in my family.
Nowadays, my primary concerns are ethical and health-related.
Whatever works for you is a result of your own self-examination and desires for your life.