Interesting. You seem to echo some of Kant’s thoughts on the topic (though he was not explicitly against exploiting and slaughtering animals, but just believed it should be done painlessly [which is obviously still violating the animals’ interests & is an act of violence & brutality by humans, and ignores all the other cruelty in the process of farming them & animal exploitation in general], so not entirely, but perhaps he didn’t even consider meat and animal product eating/using/animal use was unnecessary, and I think a form of “veganism” would be a logical extension of what he said when applying those values consistently and factoring in modern evidence and circumstances):

Immanuel Kant — ‘He who is cruel to animals becomes hard also in his dealings with men. We can judge the heart of a man by his treatment of animals.’

Basically he thought that non-human animals didn’t have intrinsic value or rights, but that their value or rights were extrinsic/instrumental to preserving and protecting human rights - sorry if this isn’t what you meant.

Immanuel Kant believed that while humans have no direct duties to non-human animals, mistreating them can be morally wrong because it can harm one’s own moral character. He argued that actions like cruelty to animals can desensitize individuals to suffering/violence and potentially lead to harmful behavior towards other humans (a lot of more recent psychological research and statistics support these assessments). Therefore, while he considered that non-human animals lack the moral status of “rational beings” (which he considered exclusive to humans, though it’s unclear if believed it to be universally true of all humans ‐ he did describe children, people with certain intellectual disabilities, cognitively declining elderly, and more prejudicially, women and non-Europeans as being less rational…), their mistreatment is still indirectly wrong due to its impact on human morality and the subsequent spillover effect that can have on how humans treat each other. I’m sure he would also be against what slaughterhouse workers are forced to deal with and what happens to those communities of people if he knew about it too (including domestic violence, aligning with the somewhat intersectionalist view of “violence begets violence/oppression/injustice/harm etc”), based on his values.

Of course, the argument from marginal cases which was proposed by people like Roman philosopher Porphyry and Jeremy Bentham - known for the frequently cited animal rights quote “The question is not can they reason, nor can they talk, but can they suffer? Why should the law refuse its protection to any sensitive being?” (and later, in modern vegan/animal rights discourse, the argument from marginal cases evolved into the Name The Trait argument, for which we have Isaac Brown AKA “AskYourself” to thank), criticized this stance and challenged its ability to remain consistent in its reasoning without taking away human rights from certain humans who possessed similar mental capacities to the non-human animals whose exploitation was attemptedly justified based on their supposed lack of rationality or lower intelligence.

Sorry to go off topic in critiquing Kant, I know you don’t agree with everything he said, but just some of the things you said reminded me of it - and those are valid points. How we treat non human animals definitely does backfire significantly on humans in a variety of ways. Where I would disagree is that I think non-human animals have innate moral value, deserving of intrinsic rights and protections, even if harming them hypothetically wasn’t going to negatively impact humans - and arguing that it does, even if true, is much harder to prove, in some cases, than recognizing the undeniable direct actions to the non-human animals. Not to be rude, but veganism to me is about animal rights (because I think non-human animals need & deserve their own movement and this is it), not human rights (even though it has positive side-effects for human rights, and human rights obviously matter, equally in my opinion, or the rights of sentient beings in general), and the idea of not exploiting animals just because of its utility in helping humans to not do so, is a very nuanced view (even going beyond plant-based environmentalism, since there are forms of animal exploitation which may not negatively impact the environment necessarily but which are still cruel to the animals, which could be opposed on the basis of it contributing to negative behaviors between humans), but I think some might consider it a form of “plant-based humanism” or “intersectionalist humanist ahimsa” or something, not sure. But, I’m fine if you consider yourself vegan (you are of course by multiple definitions), after all you’re leaving the animals alone, so that’s what matters and I respect your view :)