After I posted my list of arguments others have made for eating meat, a friend asked me the following:
Has anyone argued in favour of eating meat because raising animals produces animal lives that are worth living? Of course, on some factory farms it would not be true, but suppose that most animals’ lives are minimally worthwhile. This would justify factory farms. In which case, painlessly killing them for meat consumption would be more like a by-product of this good act (i.e., this act produces a greater amount of good). And people who like meat would also be benefited.
The answer is yes. Here's some background. In 1984, philosopher Derek Parfit published a book called Reasons and Persons, which is the most significant contribution to ethics (and other areas) of the twentieth century. Parfit's a utilitarian, so he defends the notion that morality demands maximizing well-being in the world. But there are different way to interpret maximizing well-being, one of them being to total the well-being of everything in the world. Another is to take the total amount of well-being and divide it by the number of things that can be made better or worse off. The first is the total view, the second is the average view.
Imagine we go for the total view, and suppose that there are 10 billion people in the world. Suppose also that for each person we add to the population, the average amount of well-being decreases (each person is made slightly worse off) but the total amount goes up because there are more people. So long as when we add another person to the population the total goes up, if only slightly, it doesn't matter that the average goes down for the total view.
Suppose that we've added as many people to the population as possible while increasing total well-being, such that if we add one more person the total won't go up anymore because there are no additional resources to be distributed. At such a point, however, each person's life would be barely worth living, even though the total amount of well-being would be high. In his pithy way, Parfit called this “The Repugnant Conclusion,” which he defines as follows:
For any possible population of at least ten billion people, all with a very high quality of life, there must be some much larger imaginable population whose existence, if other things are equal, would be better, even though its members have lives that are barely worth living.
His name for the result shows his opinion of it. As it turns out, he doesn't think taking the average view is a better way to go, so he finishes the chapter without resolving the problem. The reason Parfit has been so influential is not just that he has made tremendous progress in defining and working through important problems, but also that, like a mathematician, he points the way to future projects for others to take on. It's a problem that he doesn't think has a satisfactory answer so far.
All of this, of course, can apply to non-human animals. If bringing another animal into the world makes the world better off, even though the lives of each animal is made worse off, then it seems we are committed to the repugnant conclusion. Some have bitten the bullet and accepted the conclusion, arguing that it's not bad after all. Torbjörn Tännsjö, a philosopher at Stockholm University, is one of them, and he cites some others in footnote four. Many others have tried to resolve the problem in various ways, including defending the average view or one of the other myriad possibilities. I don't know of anyone who has applied it to the agricultural industry specifically, but it obviously applies.