Vegetarian who enjoyed your post here. I found your arguments well reasoned, the main sticking point to me was the marginal case argument. I would argue that our preference for and able to differentiate other humans over livestock does not defeat the logic of the marginal case argument. However, neither of the arguments you presented are the primary reason I am a veg. I hope you will consider addressing the environmental impacts of animal husbandry, I'll be there for the discussion if you do!
I enjoyed your post and included it in today’s #philosophy-review
https://steemit.com/philosophy/@aaanderson/the-philosophy-review-12-4-2016
@aaanderson: I did write up a post on greenhouse gas emissions, and how they are not the entire story. It's not a comprehensive treatment of the subject, but presents some points which I think should be included in environmental discussions but rarely are. https://steemit.com/academia/@alexbenjalbert/emission-delusion-how-focusing-on-livestock-methane-is-hurting-the-environment-and-society
As for the marginal cases, I semi-agree that the logic is sound. It uses individuals to make statements about how entire species should behave towards each other, which I find is going out on a limb. It compares the extremes of one species - e.g. an extremely intelligent pig, to someone with poor ability to reason, for instance, then makes a generalization that, on the basis of these two extreme examples, the entire species needs to behave a certain way. I don't think that is tenable if you are going to use this argument as a guide to action. In real life, the players are the entire population, with normal variation, not simply the highest and lowest 0.5% of each population. So to be truly sound and consistent, the argument should be made either using individuals and only applied to individuals, or using populations and applied to entire populations. It may make sense on paper, to some people, but it fails, in my opinion, when you try to apply it to biological systems. To be blunt, as a scientist, I honestly don't give a rat's smooth bottom if it's right on paper but we can't use it to solve real-life issues. That's why I think it's a poor argument.
Thanks for following up. I wrote a long thoughtful reply then fatfingered my screen and lost the whole thing! The long and short of it is, i agree with you that there are many important environmental issues that get ignored. However there are still reasons to belive a plant based diet is more sustainable, even beyond greenhouse gasses. I am planning to write a follow up post specifically on this.
For the marginal case, all I can say is that our outlook is different. I don't believe the treatment of an individual should be dependent on the larger group characteristics. At least not to the extent that excuses compete disregard for the individual.
From a practical perpective, i would probably sacrafice a cow life for a human life, but not so i can have it for dinner when i dont have to. Would i sacrafice a cow life to prolong the life of a brain dead human with no hope of recovery? Probably not.