The New York Times is having an essay contest (600 words, April 8 due date) on why it's ethical to eat meat.
I think the challenge is somewhat poorly defined. The challenge seems to be to argue for the thesis that it is morally permissible to eat meat when this is not necessary to human survival.
But what does the thesis mean? If it means that in all cases where human survival is not at stake it's permissible to eat meat, the answer is uncontroversially negative. For instance, when you've made a promise to a vegetarian friend not to eat meat today, it won't be permissible to eat meat on that day.
But if it means that in some cases where human survival is not at stake it's permissible to eat meat, that thesis is not particularly controversial. For instance, a typical philosophical vegetarian is unlikely to dispute that it can be permissible to eat meat from non-conscious species (worms?), accidental roadkill when doing so does not encourage further killing, or meat from a predator which one killed in the defense of one's (at least equally cognitively sophisticated) pets.
If, on the other hand, the thesis is that it's permissible to eat meat under typical circumstances obtaining in our culture, then we have to get into a messy discussion of the particular methods of meat farming in our culture, and that's the sort of discussion the contest wants us to avoid.