@OfoarHeffinsakeLogistically the diet isn't appropriate for all regions of the world. Veganism certainly isn't unless there's an alternative source of B12 that's universally available. I wouldn't advocate that the whole world should switch, but a larger ratio of vegetarians in the world seems like it'd be a good thing.As in the global warming debate, there's no shortage of contradictory statistics. The science isn't nearly as conclusive as it is with AGW. Trying to zero in on the real story is very frustrating; the beef lobbies have no qualms with cherry-picking data and neither does PETA. But as far as efficiency goes, meat production seems to have an inherent disadvantage. You need to grow crops to feed a cow, and you don't get all of the nutrients back out of that cow that went into raising it. It's true that cows are often fed the foodstock that's unfit for human consumption and would have been wasted anyway, but the fact that meat production can only get less efficient as we find ways to improve the quality of crop yields isn't a good sign. Very, very good meat production techniques could probably put the process on par with vegetable production, but in the real world many if not most of the meat production facilities won't be up to speed with those techniques. If we're interested in sustainability, why would we take the risk of adopting the food production method which already has the deck stacked against it? More water is wasted in meat production. The meat producers concede this point; they only argue that less water is wasted than vegetarians claim. And there's the pollution produced by tons and tons of manure, which, again, in a perfect world would be used as fertilizer, but usually it just goes into the rivers and causes all kinds of environmental havoc. And there's the cocktails of antibiotics and such that we inject into the cattle preemptively because the conditions they're in almost guarantee infection and disease. Much of this goes into the rivers through the urine, plus it creates an excellent environment for superbugs to emerge. Pesticides used on crops also end up in the rivers and also create superbugs of a different sort, but I think more people are scared of a new and hard to cure disease jumping to human beings than they are of a very resilient new species of weevil.The whole protein thing is just one of those myths that will probably be around forever. Getting enough protein even in a vegan diet is pretty trivial, as long as legumes are available.When you factor in the things that aren't directly related to sustainability like improved health (this is one area where consensus isn't hard to find; Americans eat too much meat) and the ethics of it all, eating meat doesn't seem to have a lot of up-sides. The reason it seems to be so entrenched in western society is a historical and a cultural one, not so much a pragmatic one.