In arguments concerning vegetarianism very often questions like the following are raised:
1) Isn't it better that an animal gets to live at all?
2) If we raise an animal and treat it better than it would be treated elsewhere (such as in the wild or in a factory farm) doesn't that make it ok?
The assumptions behind these questions seem to be (a) that an extra animal or human in the world is necessarily a good thing and (b) that one can establish the morality of ones own behavior by comparing it against a commonly occurring alternative.
I will discuss both of these assumptions and explain why I think they are false. In addition I will give answers to these questions.
Point (a): Why might we prefer a world with more animals or more humans in it? Firstly animals or people might have more companions. However, once there are significantly more animals than that animal's typical herd size size none of those animals need want for companionship. Secondly cultural artifacts (such as music, ideas and novels) are more valuable the more people there are (everybody in a bigger society has access to more ideas). However, as animals do not have the sort of culture for which this benefit exists a cow will be no happier because there are 1,000,000 cows rather than 10,000. Thirdly we might prefer a world with 1,000,000 buffalo to one with 999,999 buffalo on strict utility grounds (one extra cow to enjoy the savanna). Fourthly we may prefer a world with an extra animal because of the ecosystem services it provides. Fifthly an extra animal might be helpful towards preventing the extinction of its species.
The first two reasons are no use. The third reason is problematic because more cows mean fewer people (because, for calorie production, almost all land is better used for some crop than for grazing). See also the comments to my last post particularly with regard to dairy production as an alternative. The fourth reason doesn't justify an extra farm animal but possibly an extra wild animal. For this reason to make sense, we need to consider a national park in which the land is being used for eco-tourism or for eco-services.
However, in a world in which the slaughterhouse is banned and in which the only killing of animals is for population control in national parks (which have no natural predators left) it would be necessary to ban the selling of meat from these animals because (i) there would be not nearly enough to go around and (ii) it would introduce the profit motive which could interfere with the ecological utility of the population control and might result in greater suffering to the animals than would otherwise be the case. Furthermore by the time we are in this situation (where slaughterhouses have been banned) we may be able to control wild animal populations using advanced biotech solutions which are less problematic ethically (and potentially very cheap given the rapid decline in genome sequencing costs etc.).
The fifth reason would require the maintenance of only a few groups of the animal in question. These populations could be held in check relatively cheaply by confining them to small national parks and sterilizing a large percentage of the animals.
Point (b): The correct comparison is not between an animal raised in captivity and an extra animal in the wild but between an animal raised in captivity and an extra person (not 1 animal per 1 person though). If we had fewer animals in the food industry we would have more people not more wild animals.
So now my answers to questions 1 and 2. (1) An extra animal generally means fewer people and so we should prefer raising fewer animals (this may sound strange from a vegetarian but as I've pointed out animals aren't any happier by virtue of there being many of them). We should maintain each species (which can be performed fairly cheaply) and we may need to maintain animal populations in national parks but we should put research into finding ways of doing this that do not boil down to killing animals. (2) This is offering a false comparison. One should try to provide the best life for people and for animals and saying that their life is better than it might be under some other circumstance should be no excuse.