Simon Fairlie argues, contra vegans, that eating meat isn't bad in itself. It's current farming models that deserve our ire, not their product. From the Guardian (via Kottke):
Efficiency is the ratio of useful work performed by a process as compared with the total energy expended. What we slot into those boxes says everything about our values. What vegans (the ones worried about efficiency) are up in arms about is that large tracts of arable land are being used to feed cows instead of people. Fairlie is saying that needn't be the case, and it would be best to compare the overall amount of land dedicated to growing food for humans in each case.But idiocies [like feeding human-edible grain to cows], Fairlie shows, are not arguments against all meat eating, but arguments against the current farming model. He demonstrates that we've been using the wrong comparison to judge the efficiency of meat production. Instead of citing a simple conversion rate of feed into meat, we should be comparing the amount of land required to grow meat with the land needed to grow plant products of the same nutritional value to humans. The results are radically different.
If pigs are fed on residues and waste, and cattle on straw, stovers and grass from fallows and rangelands -- food for which humans don't compete -- meat becomes a very efficient means of food production. Even though it is tilted by the profligate use of grain in rich countries, the global average conversion ratio of useful plant food to useful meat is not the 5:1 or 10:1 cited by almost everyone, but less than 2:1. If we stopped feeding edible grain to animals, we could still produce around half the current global meat supply with no loss to human nutrition: in fact it's a significant net gain.
It seems like there's a problem here. Vegans say that if we stop feeding human-edible grain to cattle, then we reclaim all of that land for growing human food. Fairlie is saying that we can do that -- and have our cattle too. We'll just have the cattle eat something else, something humans don't eat, like grass. But that land was doing something else before -- it's not as though there's an infinite amount of arable land just waiting for cattle to be put on it. We've gone from a system in which X acres feed humans directly and Y acres feed the cows that feed humans to a system in which X+Y acres feed humans directly, and Z acres feed the cows that feed humans. That's a net increase in acres, but whether there is a proportional increase in food for humans is complicated even in a simplified grain-and-cows model.
Part of what Fairlie is suggesting is that better (meaning more robust, sustainable, and efficient by some measure) agricultural practices would by their nature produce an opportunity to feed cattle: instead of dumping nitrogen onto the same fields year after year, we would actually rotate crops, and at least some of the crops in rotation would be food for cattle and not for people. But these better practices (and I agree that they are better) require more land to produce the same yield.
More than likely, Fairlie discusses much of this in the book (I haven't read it), so I don't mean to impugn him. I simply want to point out that this is a hard problem, and one whose solution depends on a fair bit of empirical work.
For most people who worry about such things and want to do something about it, the only plausible choice is to stop eating meat.