I've noticed that whenever people talk about "humane treatment" they're usually referring to either nonhuman animals or humans who are imprisoned or otherwise institutionally confined and controlled. I guess this makes sense since keeping people in cages and under complete control resembles how nonhuman animals are general treated in our society. Similarly, the term "cruelty" is usually applied to the treatment of nonhuman animals, human children, and human prisoners. In fact, "humane treatment" and "cruelty" are really paired terms, with the former suggested as the remedy to the latter.
I think this talk about "cruelty" and "humane treatment" is basically a way of depoliticizing oppression. While focusing on "reducing harm" or "reducing suffering," these terms fail to address the oppressive power relations under which harm and suffering occurs. These terms take the existence of human supremacy and the prison industrial complex as a given. That is, the domination of nonhuman animals and human prisoners respectively is deemed appropriate; efforts are directed to minimizing harm and suffering rather than abolishing the oppressive power relations.
Focusing on suffering and cruelty, and calling for humane treatment, doesn't address the structure of oppression. So I think it's important to recall that the vegan movement was founded on principles of opposing, and developing alternatives to, exploitation (particularly where humans exploit other animals). Unlike "cruelty," the term "exploitation" denotes a power relation between an exploiter group (e.g., humans) and the exploited group (e.g., nonhuman animals). Where as cruelty "can be regarded as a pattern of socially and culturally unacceptable behavior," exploitation marks "the material and psychological gains" that come to a more powerful group, "which are bolstered by an ideological support system" that forms the basis of what is socially and culturally acceptable.
Unlike "humane treatment," the vegan ideal of nonexploitation is linked to principles of anti-oppression. That is, veganism calls the "the material and psychological gains" of human privilege into question; its primary aim is to eliminate the system of human supremacy. In contrast, under the concept of "humane treatment," human privilege goes unquestioned; this concept only seeks to reduce harm or suffering that occurs under a system of human supremacy.
I find parallels here between veganism and prison abolition. Both call out the political relations of oppressions that are usually masked and depoliticized with similar terms. That is, both reject the calls for more "humane treatment" under the existing system.
Also, both prisons and the exploitation of nonhuman animals are often justified on the basis of "human nature." People who argue for the "humane treatment" of human prisoners or nonhuman animals usually can't conceive of a world where humans aren't imprisoned or without the exploitation of nonhuman animals. Or they simply refuse to believe that such a world is desirable. However, veganism and prison abolition both show that the society we live in determines whether these forms of oppressions exist, and they both work to present a vision of what the world would look like without these oppressive power relations.
In the spirit of honoring the efforts of all who are striving for the emancipation of humans and of other animals, it is important that vegans support prison abolition. The prison industrial complex and the exploitation of nonhuman animals are connected through a rhetoric of "cruelty" and "humane treatment," and veganism and prison abolition are connected by a commitment to anti-oppression. Moreover, there seems little sense in eliminating a system that imprisons and controls nonhuman animals without working to eliminate a system that similarly imprisons and controls human animals.