After reading some discussion on lemmygrad about veganism, I felt the need to share my thoughts in a separate thread, as comments weren't appropriate for the wall of text I'm about to throw.
Before we start, very important precision. This is not about environmental veganism, only about animal-liberation veganism. Consuming less animal products will be a lifestyle change we must anticipate to limit environmental destruction. This is about the moral philosophy of veganism and its contradictions with materialism.
Intro
Veganism is often rationalised under the form of a syllogism : it is immortal to kill and exploit humans, and non-human animals are equal to humans, therefore, it is immoral to kill and exploit non-human animals.
Now, I must say, if one is to contest the validity of this syllogism as a basis for veganism I encourage them to provide one since it could drastically change my point of view.
Like many syllogisms, there is appeal and validity to it until you question the premises. Let's review them under a materialistic lens.
Morality and materialism
The first premise is that it is immortal to kill and exploit humans. As leftists, we tend to wholeheartedly agree with such a statement, as it encapsulates our ambitions and dreams, however this cannot be pursued for a political manifest beyond utopian wishful thinking. Historically, killing has been justified as a high moral act whenever the one being killed was deemed worthy of death. The reason it is generally considered immoral to interrupt one's life is because humans simply have to collaborate to survive, therefore every society has developed a social construct that allows us to live as a social productive species. But whenever a war enemy, criminal, or dissident person is being killed under certain circumstances, the killing becomes justified, morally right.
As materialists, we don't base our interpretation of morality on a notion of some metaphysical, reality-transcending rule, and even less in relation to an afterlife. Morality is a human construct that evolves with material conditions. In that case, the relationship of human morality with non-human animals becomes more complicated than it seems. Humans do have empathy for other species but are also able to consume their flesh and products, a contradiction that has defined the construction of morality around non-human animals through history. This explains why it seems desirable for a lot of people to stop unnecessary animal cruelty while still wanting to consume their flesh, there is an act of balancing between empathy and appetite.
Equality of species and violence
Now you might have noticed that this framework is definitely human-centric. That brings us to the second premise, which is the equality of all species. By all means, it is absolutely outdated to maintain the idea of "human superiority" on all non-human species in the current times. As materialists, we should realise that humans evolved at the same time as other species, are dependent on the ecosystem, and that there is no fundamental variable that we have to consider as a criteria for ranking in an abstract "order of things".
That said, the equality of all species doesn't automatically mean the disappearance of inter-species violence. Firstly, we cannot stop unnecessary violence between fellow living beings that don't share our means of communication (unless we exerce physical control over them, but that's even worse). Secondly, there is an assumption that only humans possess the ability to choose to follow a vegan diet, which is extremely strange considering that it makes humans the only specie to have the capacity to be moral. Either non-human animals are excused for their chauvinistic violence against other species because they are seen as too limited, determined by their instinct, but it makes humans actually morally superior to other species. Or the animals must be held accountable for inter-species violence, which no vegan upholds, thankfully. Last option would be to consider that inter-species violence is part of life, which I agree with and think is the materialistic approach, but that means there is no reason to adopt a vegan diet.
Conclusion
So what does that let us with? Morality being a social construct with a material use in a human society, and humans being fundamentally empathetic, it is completely understandable that society will be progressing towards diminishing meat consumption to allow the minimization of animal suffering. But the exploitation of animals as means of food production doesn't have a materialistic reason to go away (unless we're talking about climate change, of course). The inter-species violence of humans against cattle and prey is part of nature, because we simply are a productive omnivorous specie just like any other.
This is mostly why I would discourage pushing people to abandon all animal products in the name of ethics. What should be encouraged is acceptance of every specific diet, be it religious diets, or animal-liberation diets. Strict vegetarianism must be a choice of heart that is based on profound empathy, not a superior moral choice or, worse, a moral imperative.
Fwiw this isn't always true. Chickens will produce plenty of eggs without needing to give them any kinds of hormones, which are largely for meat production regardless, not eggs.