First- there's a famous article by Peter Singer from which most of the arguments in this blog are directly taken or at the very least inspired by. See it here: http://www.utilitarian.net/singer/by/1979----.htm

Peter Singer is a utilitarian. Very broadly speaking, this means that 'the fundamental moral principle is to take actions which maximize general happiness.' What I want to distinguish from the outset here, though, is that whether you are a utilitarian in general or Singer's particular version, or anything else, one of the main arguments in Equality for Animals still holds for you.

That was to get your attention. I mean something a bit more precise. First, if you choose to accept Singer's utilitarianism, then it's abundantly clear that you are committed to not eating meat, at least of "sentient" creatures. Sentience means something like 'the ability to feel pain or pleasure' and presupposes some type of central nervous system with which feeling gets done. Sentient: cows, pigs, goats, chickens, probably some fish. Not sentient: rocks, potatoes, kale etc. Probably not sentient: clams, mussels, bees etc. It should also be noted here, that not all sentient things get "counted" equally here; it's worse to harm a cow than a chicken in virtue of the fact that the cow has a more developed nervous system/emotional apparatus. Singer also makes a strong case that if you call yourself a utilitarian of any flavour, then you are going to be committed to considering the interests of (sentient) animals in some fashion (which might be slightly different from his own).

I don't care (for the purposes of this blog) about any of Singer's arguments which suppose any form of utilitarianism as premise. What I am concerned with is a more modest argument from Equality for Animals which I'll call here the Argument from Marginal Cases (AMC).

The AMC is an example of a type of argument I'm calling (and this might be standard, I'm not sure) an argument from consistency. Arguments from consistency take as premises beliefs we already hold and derive from them a contradiction. If we are rational people, we are faced with a dilemma: either one belief or the other leading to the contradiction must go (after all, we can't say we believe 'X and not X'). I think I like arguments from consistency because of my empiricism (their premises are taken from a description of our actual beliefs). They also tend to be straightforward to argue, without a lot of logical filigree.

Preamble aside, here's the Argument from Marginal Cases (AMC):

First premise: Making moral judgments on the basis of purely physical properties is unjustified and constitutes a moral wrong. By 'purely physical properties' I am trying to string together some words to gather up all of the "isms" - racism, sexism, etc which we think are wrong. For an example of an unjustified judgment 'Only white males should be able to vote.' Being white and male does not endow one with any praise or blameworthy features (note: you should separate physical characteristics like 'whiteness', 'maleness' from cultural characteristics in order to make this clear) in of itself - for instance white males do not have larger and more sophisticated brains or some special talent at voting well on the basis of their whiteness or maleness. As a corollary to this, we may sometimes assign praise or blame on the basis of other properties (for instance, mental development, intelligence etc). To use the voting example again, we might say that only people who can pass a test on citizenship should be able to vote. Note though, that this corollary is not necessary for the argument, I'm just adding it to round things out a bit!

Second Premise: It's wrong to torture, kill, or eat a mentally disabled human or a human infant.

Third Premise: Eating meat is morally permissible in the ways we currently consume meat: for example buying ground beef in the supermarket for dinner.

Argument: Many of the animals we habitually eat (pigs, cows) have equivalent mental capacities to severely disabled humans and infants/young toddlers. I want to make it clear that this is just a fact- if you want to disagree here go read the relevant science. If we accept premise two, we think it's wrong to do things like factory farm mentally challenged humans for our gustatory pleasure. But if we accept premise three, we think it's totally OK to factory farm things like cows for our gustatory pleasure. But if cows have the same relevant mental capacities as the marginal humans we don't factory farm, then the property with which we decide what to factory farm and what not to factory farm seems to be the property that cows look like cows, and mentally challenged humans look like humans. 'Looking like Cow-ness' and 'Looking like human-ness' are clearly purely physical properties. But if we accept premise one, purely physical properties are not acceptable for making moral judgments (and what/what not to kill for our gustatory pleasure certainly constitutes a moral judgement!).

Conclusion: So by P1, either it's acceptable to grow and eat marginal humans and all animals, or it's acceptable to grow and eat neither. But we hold P2 and P3, which says that it is acceptable to grow/eat all animals but not all marginal humans. Therefore, holding P1, P2 and P3 results in contradiction.

So here's the difficulty. We can resolve our contradiction by giving up P1 P2 or P3, or we can resolve the contradiction by finding a flaw in the argument. Which premise is it easiest for people to give up and remain rational/consistent? Where is the flaw in the argument?