It is a factor I think about; I'm not saying that it's never ethical to eat meat; I don't condemn a lion for eating an antelope, since I'm not even sure it's possible for a lion to be a vegan if it really wanted to [0]. Similarly, I don't have a problem with birds being carnivorous.

That said, anyone reading this post is probably not a lion or a bird, and has some level of self-reflection as a result. Just to play devil's advocate for a bit, couldn't you argue that if it's possible for me to live a fairly healthy life without killing any higher-minded creatures, then I should? If we are smart enough to have an entire philosophy of ethics, then shouldn't we be using this ethical framework to minimize suffering in the world?

I should reemphasize, I'm not a vegan, or a vegetarian, I have a fairly typical American diet of "it's not a meal without meat" sadly. I'm just saying that these kinds of papers make me question that.

[0] I'm not a biologist or doctor or anything, but my understanding is that cats (at least house cats) cannot product their own vitamin A out of Beta-Carotene like humans can, and must get it out of animals. I certainly cannot blame any animal that is doing what it absolutely has to for survival.

Thanks for the thoughtful response! To be clear, that wasn't a loaded question -- as someone who hasn't thought too hard about this, I really did want to hear your opinion. :)

I believe humans still require vitamin B12 which we can only get from meat, however you can supplement this via plant-based milk and other ingredients.

B-12 is most readily available in meat, but is bio-available to reduced/smaller levels from non-meat sources (e.g. some fungi and algae).