Thanks for your post. It contains a number of substantive points and I'll try to address them as best I can.
Do I think it's inconsistent to argue against racism etc but not against speciesism? Not necessarily. It depends on the reason given. Usually the reasons given are inconsistent. If somebody argues against racism because we should treat all humans equally then the question arises '
what about non-humans?' The answer to that can range from Descartes' answer that they merit no consideration whatsoever, to Gary Francione's 'animal abolitionist' answer that it is
never acceptable to use animals any way, even when they don't seem to mind being used. Francione is so far along the spectrum that he seems to regard Peter Singer as pretty close to a battery poultry farm operator.
Some religions proclaim that humans merit special consideration, in fact so much so that a single-cell fertilised human ovum is accorded greater consideration than a chimpanzee or other advanced non-human mammal that clearly has personality, preferences and an sophisticated ability to communicate. The justification given is 'God says so'. I find nothing inconsistent in that. It's just that I don't believe God (if there is one) does say so, so I respectfully disagree with the holders of such beliefs.
Bernard Williams' ethical perspective, elucidated in a thought experiment involving super-advanced aliens taking over the Earth, is that it is ethically defensible for humans to favour members of the human species because it is
our species. Such an approach may or may not be inconsistent depending on the approach taken. It depends on the response to the question 'Why is it OK to favour animals of the same species as you over other species, but not OK to favour animals that have the same species and ancestral homeland over animals that have the same species but a different ancestral homeland?' An answer which avoids inconsistency, at the cost of embracing arbitrariness, is '
Because in my ethical framework, species is all that matters in determining the circle of concern'. Bernard Williams was happy to (in fact often seemed to relish) taking on defiantly arbitrary-seeming positions like that, and his position is unassailable. But most people are not comfortable withthat position. I think most people would instead try to argue that the level of concern 'owed' to others drops off gradually with distance, rather than dropping from everything to nothing at the border of a species. That's fine, but it does have the uncomfortable consequence that, since people of African ancestry and people of Northern European ancestry are less closely related to those in the other group than to those in their own group, it ethically justifies a small, but perhaps measurable, discrimination by a member of one of those groups against members of the other. Most people are not comfortable with that. I know I'm not.
Another possible argument is that what matters is things like awareness, ability to communicate or being able to think about other people's thoughts. That would be fine if people really believed it, but my impression is that they don't. A newborn baby scores much lower on those considerations than do most mature members of the higher mammal species, yet most humans would accord greater consideration to a baby than to an adult chimpanzee.
It seems to me that, to avoid inconsistency, an argument for giving all humans greater consideration than all animals either has to just declare as axiom that species is what matters (or some other arbitrary factor, like 'potential personhood', which is an issue sometimes raised by religious people that feel embarrassed to explain their human-preference just by 'God said so'), whether for religious reasons or out of feisty Williamsesque defiance, or accept that the approach implies lesser consideration for humans with whom we share fewer ancestors. But that may just be my lack of imagination about the types of arguments that can be offered. I'd certainly be interested to hear of possible alternatives.
You also asked '
what counts as an ethical reason? Well that's a huge question, and I think many different types of answers would be offered by different people. I suspect that 'ethics' may be one of those concepts that can only be characterised by Wittgenstein's 'family resemblance', eluding attempts to agree a generally accepted definition. But one thing that I think most people would agree on is that ethical decisions form only a small part of all the decisions we make. So any attempt to characterise ethical considerations that includes considerations that would drive a majority of decisions would fail to meet most people's idea of what ethics is.
I think that Πετροκότσυφας's suggestion of 'a practical organising of our relations' would fail on that score. Such a phrase encompasses making allocations in a Christmas Kringle, making introductions at a cocktail party, writing emails, letters and forum posts, applying for jobs... In fact nearly all the things we do seem to fall under that heading, leaving aside only those items that involve only one person - playing patience or working on a maths problem perhaps.
Of course there's never any point in arguing over definitions. If somebody wants to adopt a definition of ethics that includes deciding who to get to run the anchor leg in the 4 x 100m relay, I wish them joy of it. But their idea of ethics will be so far removed from mine (and I believe also from that of most other people) that it would be pointless to attempt to discuss any purportedly ethical issue with them.
For me, and this may be just me, the domain of ethics seems to be delineated by the simple consideration that it is about making decisions that I expect to have an impact on the feelings of other beings that I believe to be sentient.