Additional proof that you are not a stereotypical liberal, or you'd know this one. ;)

The simple answer is that treehuggers would oppose consumer excess simply because that's part of the philosophical package, which includes a bone-deep hostility toward fast food corporations of any kind.

The more complex answer is that good environmentalists decry the use of good land to raise food for farm animals when it could be used for forests or growing soybeans for people to eat.

Actually, there is a good point somewhere under all that. In the history of human agriculture, the purpose of a cow was to run around the plains, eat and digest grass and other cellulose-filled vegetation mostly indigestible to humans, and concentrate it conveniently into forms of nutrition that humans could eat (meat, milk). Feeding a cow corn, grain, or other edible vegetables kind of misses the original point. Feeding them ground-up cows is downright stupid, and has been a source of the mad cow problem.

Interestingly, McDonalds has been in the forefront of good farming practice for years, and often been the first to mandate that the meat they buy meets certain specifications in that area. And when McDonalds makes a rule, the farmers damn well listen.