The consumption of meat is one of the main causes of environmental degradation and devastation. Animal livestock uses approximately half of the water consumption in the United States. A diet that centers on meat creates a need for about 4,500 gallons of water per day, per meat-eater, as compared to 300 gallons per day for a vegan (a diet of no flesh or dairy). An animal based dies requires approximately eighteen times more energy to sustain than a plant-based diet. The destruction of the rainforest for grazing land, and the resultant greenhouse effect is one more case of the harmful effect of a flesh-centered diet on our environment.
Animal products are at the top of the food chain having about 15 times more pesticides and herbicides than fruits and vegetables.
(Ok maybe that is about 3 reasons.)
Just food for thought.
This information was taken from several very recent publications and books.