I am a humanist, which is to say at least two things: I've spent more than half my life in the humanities; and, while I don't know that we always get the right result, I believe that moral questions must be addressed from the human perspective—after all, there is no other perspective we can successfully take. (This is not to say either that only humans matter or, in the style of secular humanists, that religious values cannot be discussed or considered.)
But the right kind of humanism cannot be that sort in fact exhibited by those who claim to be religious (and often deride humanism) but demonstrate in many of their beliefs an inheritance from the Enlightenment and its immediate intellectual forebears, namely a vision of humans as divorced wholly from the rest of nature. I call this, too, a kind of humanism inasmuch as it replaces a presumed God of creation with a God of humanity. If that's not humanism of a sort, it's hard to know what it is.
Consider two fonts of this sort of view: Descartes and Kant. In his dualism, Descartes endows humans with a mind. He is at pains to distinguish this from the soul (the anima that animates all animals). He goes out of his way to deny this mind is shared at all by the (other) animals. Here, in a new way, we are separated from the rest of nature. Nature is simply a mechanistic body devoid wholly of mind, while we are minds. Of course, we have bodies, but this is not essential to us.
In Kant's conception of the human being, we are defined by two characteristics: our will and our reason. It is these two things that make us what we are and it is their lacking in the natural world that makes that world morally irrelevant. The natural world, the phenomenal world, is deterministic and unreasoning. Only we are free and reasoning and only as we are conceived in the noumenal world, not the world we sense. And, for all the sublimity with which Kant enchants the natural world, this is nothing more than a power to create an effect in us.
I'll not delve too deeply into the consequences these views have for treatment of nature and animals. But, it should be obvious that on such views, nothing can be wrong per se in any treatment of the non-human world, except as it affects humans. Torturing a dog like Heathcliff is wrong not because of the dog's suffering, but only because if might lead to insensitivity to human suffering.
Rather the pervasive problem is in seeing us as divorced from nature. This contrasts an older tradition—that tradition against which Descartes rebelled—that sees humans as ensconced in nature. Even Plato for all his hatred of the physical world, sometimes hints that the physical world's other inhabitants might have a deeper connection to us; or, at least one might infer this from some of his considerations of metempsychosis. Surely Aristotle, in his views of the souls we share with other living things: the vegetative and animal—and in his tying together of form and (physical) matter and placing us between, but sharing in the natures, both of God and the animals, places us as much more firmly in nature. This is a theme mirrored in the Stoic belief that all living things share in a piece of the fire that permeates the Universe as well as the ancient and medieval mindsets in which humans can learn moral lessons from natural history and bestiaries.
I'm not just being an old codger here nor am I arguing that animals stand on the same level in moral consideration as we do—I am, after all, claiming to be a humanist, to place humans first. But there is something disconcerting about having to argue with University students who firmly believe that "All humans are animals" is false; with people who tell me that something ought to be done about the birds—the parrots, the hummingbirds, the eagles and hawks, etc.—on campus, because they have the temerity to defecate on car hoods; to watching student overcome with disgust and fear at the lizards, possums, raccoons, mice, rats, etc. that come up from the canyons on the side of campus (it's lucky they don't see the coyotes in the daytime); at having students strenuously deny the possibility of natural selection less out of religious conviction that out of concern over human dignity; and, at having those students who accept evolution conversely claim that because we are a different species, we may exploit all the rest of nature.
What am I claiming? Just that a view of humanity that sees us as apart from nature is an impoverished one, impoverished in its appreciation of the natural world—not just in zoos and botanical gardens—as a good in itself and impoverished in its appreciation of what we are as part of that same nature. To see ourselves as angels trapped in bodies is as wrong and harmful as to see ourselves as merely clever pigs. Perhaps we need a return to the Great Chain of Being—in a modified form—to see our place in relation to and in nature.