I didn't read much of the report from which this is sourced from, but it appears that they base their numbers on current farming practices. In the U.S., those practices (for beef, pork, etc.) are, for the most part, horrible and irresponsible. Responsible practices work in concert with and support of the environment, not against it. Cows graze on and replenish lush grasslands. Pigs forage through and replenish forested areas. The animals are allowed to work within the cycle of nature and act as integral parts of healthy land management instead of being removed from it and treated as industrial outputs.

Cows aren't the problem. Pigs aren't the problem. Chickens aren't the problem. Mankind's industrialization of cows, pigs, and chickens is the problem.

So, for me, that's why we're still having this debate.