Man, beast, and the big lie
I've held for many years that the one great central error in all of human thinking is the belief that humans have souls. That is the original error from which all our other errors flow.
This question here -- the ethics of meat-eating -- is a good example. Most people's thinking about it starts from an unstated premise that there is a qualitative rather than quantitative difference between humans and other animals -- it's not just that we're more intelligent, more emotionally sophisticated, have more elaborate social organization, etc. than other species (just as some other species are "more" each of those things than yet other species -- we're at one end of a spectrum). It's that there's some kind of fundamental, un-bridgeable gulf of difference between, on the one hand, one particular great-ape species, and on the other hand, the other four great-ape species and all the other animals in the world. Everything from the chimpanzee to the dust mite is in one class, we're alone in the other.
This is biologically absurd, but it's taken deep root in our thinking, even in our language, as in the use of "humans" and "animals" as contrasting categories, as if the former were not a subset of the latter. "Humans have rights, but animals do not" is obviously a mere statement of dogma rather than a description of reality -- but beyond that, the more subtle error is in the very categories themselves. To state the same stance realistically -- "One animal species has rights, all other animal species do not" -- would at once force attention toward all the real questions that such a stance raises.
Today millions of people who would consider cannibalism (and certainly the systematic raising of humans to be slaughtered for food) to be an unspeakable outrage, have no qualms about eating bacon; many of those who would march in the streets to protest inhumane conditions in Guantanamo are unmoved by the far more inhumane conditions in factory farms. This is only possible because of that fundamental error in our thinking, that other animals are not just our inferiors in degree but are somehow fundamentally different, not the same "stuff" as we are, so that their sufferings -- and, yes, rights -- can simply be ignored as if they did not exist.