Vegetarian diets are very appropriate.
A good start for info is: http://www.goveg.com/theissues.asp
Amongst points raised are the following;

More than 27 billion animals are killed for food every year in USA.
Imagine the number worldwide, and wonder if each animal is killed humanely.

Farmed animals are no less intelligent or capable of feeling pain than are the dogs and cats we cherish as our companions. They are inquisitive, interesting individuals who value their lives, solve problems, experience fear and pain, and are capable of using tools.

Vegetarian foods provide us with all the nutrients that we need, minus the saturated fat, cholesterol, and contaminants that are found in meat, eggs, and dairy products. Plant-based diets protect us against heart disease, diabetes, obesity, strokes, and several types of cancer. Vegetarians also have stronger immune systems and, on average, live 10 years longer than meat-eaters do.

More than half the water used in the United States goes to animal agriculture, and since farmed animals produce 130 times more excrement than the human population does, the run-off from their waste greatly pollutes our waterways.

Raising animals for food is extremely inefficient—for every pound of food that they eat, only a fraction of the calories are returned in the form of edible flesh. If we stopped intensively breeding farmed animals and grew crops to feed humans instead, we would easily be able to feed every human on the planet with healthy and affordable vegetarian foods.

Factory farms pollute the air and water for many miles in every direction, often spreading contamination and illness to the people who live and work nearby. Chronic sickness, brain damage, poisoned waterways, elevated cancer rates, and even death plague these communities.