http://www.nytimes.com/2008/01/27/weekinreview/27bittman.html?pagewanted=1&ei=5070&en=a1087de0ce76df87&ex=1202187600&emc=eta1This is a really nice article about the current and up-coming problems caused by people (particularly upper- and middle-class Americans) eating too much meat. For example, they talk about the health problems, environmental problems, and the rising cost of raising/feeding livestock that'll be passed onto the consumers.
I should point out that the author isn't vegetarian, and he's not telling people to stop eating meat. Rather, he's suggesting that people eat less meat, and, when they do, to try and eat non-factory-grown meat.
Then there's also this angle, which I like a lot:
Though some 800 million people on the planet now suffer from hunger or malnutrition, the majority of corn and soy grown in the world feeds cattle, pigs and chickens. This despite the inherent inefficiencies: about two to five times more grain is required to produce the same amount of calories through livestock as through direct grain consumption, according to Rosamond Naylor, an associate professor of economics at Stanford University. It is as much as 10 times more in the case of grain-fed beef in the United States.