I became a vegetarian in July after thinking about it for a long time. The main reasons for me are:
1. I wouldn't want to kill animals myself in order to eat them, and I don't want to eat something that I would feel morally incapable of supplying for myself.
2. Animals are mass-produced for slaughter and not treated well while they are alive, and not killed humanely.
3. Animals take a huge amount of space and resources to be produced, slaughtered and brought to stores, from the space, time and resources it takes to grow the food they eat to the animals themselves. Many fossil fuels are wasted in this process, especially in shipping (of course this last could be said for many fruits and veggies too).
But here's a new reason: the Grist, an online environmental magazine, wrote this article today about poultry production. Apparently large poultry corporations are buying cheap land in the rural south, paying people incredibly low wages to raise the chickens, and sidestepping many environmental and health concerns for the people of the areas around these new chicken farms.
So now not only is vegetarianism an animal rights issue, but also a human rights one. I knew this before, but this just brings it to the fore again.