There is a fantastic report out by the Environmental Working Group that shows why we all need to be eating fewer animal products--both meat and dairy. You really have to check it out there are all kinds of cool factoids and graphs.
Like this one--if everyone in the U.S. ate no meat or cheese just one day a week, over a year, the effect on emissions would be the equivalent of taking 7.6 million cars off the road.
Another interesting fact, a 2009 National Cancer Institute study of 500,000 Americans found that the people who ate the most red meat were 20 percent more likely to die of cancer and at least 27 percent more likely to die of heart disease than those who ate the least. Another study found that those who ate the most processed meat had a 67% higher chance for pancreatic cancer then those who ate the least.
And for those concerned about their weight, this section will be of interest:
Recent research suggests that eating all this meat is contributing to the U.S. obesity epidemic. Several major epidemiological studies have found an association between high meat consumption levels and being overweight. A 2009 Johns Hopkins University study found that those who consumed the most meat consistently ate an average of 700 calories more per day and had a 27 percent greater likelihood of being obese than meat eaters who consumed the least (Wang 2009). Another large-scale European study found that men and women who ate the most meat consumed an average of 900 and 600 more calories per day, respectively, than those who ate the least. The study attributed weight gain to the high fat content and calories in many meats and concluded that “a decrease in meat consumption may improve weight management” (Vernaud 2010).