I like my barbecue. I like my smoker. That said, I spent 4 days as a vegetarian last week. I thought that was a good genuflection while reading Eating Animals by Jonathan Safran Foer. The book is his exploration to understand the place of carnivory in our world. It's a Jewish approach to the topic--"to understand is to question"--and generates a multi-faceted view of the topic that examines cultural, health, economic, and environmental questions. It's a book that is as tough to put down as it is to keep reading.
The environmental aspects are worth noting here. He summarizes well the environmental costs of modern factory farming (and fishing). Its externalities born on society and the environment are not trivial. For example, he writes "At one point, three factory farms in North Carolina were producing more nitrogen...than all the crops in the state could absorb". He also notes that the UN's FAO recently stated that farmed animals contribute more to climate change than the entire transport sector.
The environmental costs of raising and eating animals has fallen through the cracks largely in the ecological community. For example, we study N eutrophication of systems, but less often study the social, cultural, and economic forces that generate them. Governments have often punted on this issue, which then means scientific societies have to stretch to fill the gap.
Most noteworthy in the book, for all the environmental costs of raising animals in a factory setting, the marginal cost of raising pigs in pasture: 5 cents a pound.