First, I will say that I think the Animal Kingdom -- and, in fact, all of life on Earth, whether animal, plant, or Fungus - is beautiful. Animals are innocent. They go to Heaven, according to Isaiah 11:6-7. If they ar not in Heaven, I don't want to go there. Yet we humans create a Hell on Earth for them, which is deeply wrong. Years ago I read the books by seminal eco-theologian Thomas Berry on the spirituality of reverence for nature and moving from an anthropocentric to an ecocentric worldview. But well before that, I loved dogs and loved nature when on canoe trips. I have four dogs now and also recently started fostering dogs. I get only rescue dogs (as Bob Barker on The Price Is Right used to say, "spay and neuter your pet"). As I write this, my beagle Rosie is waiting patiently to jump on my lap for a hug ... Okay, the hug is done ... I love the nature videos by Habitat Forge (how to create closed ecosystems in jars) and Nature World Facts (deep-sea creatures).
Here is where ethics fits into it. Science and reason shaped my views on this to some extent. Homo sapiens are a type of animal, which is a biological fact. This fact has ethical implications. It means we share existence on this planet with other animals who are more like us than we often tend to acknowledge. So I am for humane alternatives to industrial animal agriculture, which is unbelievably cruel and environmentally destructive as well. I wrote a science paper on the latter topic a few years ago that was published by Science for Peace (though I can't find the link now as their archives go back to just 2020).
Animals caught in this vast factory farm machine definitely feel pain; they have individual personalities (pigs are said to be more intelligent than dogs), and some animals (all mammals certainly) have the same capacities for emotion that we have. Many animal species dream, meaning that they have REM. Some make moral decisions and exhibit altruism. This has been demonstrated by animal behavioural scientists. See the books by biology professor Marc Bekoff on this.
Should they be treated instrumentally, like objects, as things in a machine? I would say no. We too are collections of cells, but we are also persons. We share a social contract not to harm each other (in most circumstances) for the sake of mutual cohabitation. In practice, we extend this concern to a degree to pets through animal welfare laws to protect them, though they are still considered property, despite that. But these laws do not apply to animals slated for agricultural use. This contradiction in the law -- in how we treat similar species very differently - is the result of economic interests and politics, not the use of reason or morality or fair application of the law. If we treated a dog as we treat cows or pigs, we'd be arrested.
What about insects then? Sentient animals include mammals, birds, reptiles, possibly fish and some invertebrates like the octopus (which exhibits intelligence). Non-sentient animals include insects and microbial life. This is the rational dividing line. Placing the dividing line on human versus non-human is arbitrary. It is mere tribalism. It has been compared by some ethicists, including Tom Regan and Peter Singer, to placing the interests of one homo sapien race against another and using them instrumentally, as objects, not persons. As for insects and non-sentient animals, we should not use them badly either (though I have no great love for ticks or mosquitoes when they bite me :)). The applicable ethic here is Albert Schweitzer's Reverence for Life and the principle of non-harm. I would not go as far as Jains on this point, but nor do I kill insects, and if I see worms or insects drowning, I save them. They are amazing too! Imagine being in their place.
I spent most of my life not caring about animals at all -- and in fact used to hunt them with my father, and we were big meat eaters -- but when in grad school, I happened to read Tom Regan's books, which use entirely rational arguments; I had to change my mind. I got my doctorate in philosophy of religion and was trained by that time to see issues through the lens of practical ethics. Regan, an ethicist, persuaded me. See his most accessible book, Empty Cages. In it, he argues that other demonstrably sentient animals are in the world and aware of it. What happens to them matters to them even if to no one else, and that should matter to us as creatures who have so much power. With power comes responsibility, not just a right to abuse it for our own ends.
Then I also learned about the Non-human Rights Project, which does legal cases for individual dolphins, whales, and chimpanzees, and makes strong arguments that they are individuals who deserve basic rights, not enslavement or harm. Some judges, when it goes to court, agree with this but limit their rulings to just that individual because they know that the implications of acknowledging the personhood of all mammals would raise a political firestorm when applied to cows and pigs. These judges let politics influence them to a safe position.
Biologically as well, humans are omnivores on the fruitarian side of the spectrum like other great apes, our cousins. Dogs are on the carnivorous side of it. We can thus easily be healthy without eating meat if we get protein and iron from plant-based diets. We are not obligate carnivores like cats, for example. So that presents us with a rational and moral choice.
I am all for lab meat and plant-based meat alternatives, some of which are quite good. This position can be defended rationally with reference to science, such as animal behavioural science and environmental science. We tend to be defensive when this issue comes up, but if you put that emotional response aside and look at it rationally, species discrimination doesn't make sense. We share a planet with other sentient beings in the vastness of space but overlook them, as though they are things to be used. If alien life were discovered, we'd be amazed, but why are we not amazed by life here or the fact that we are surrounded by sentient beings? We took a different evolutionary path, but that does not make us superior or entitle us to use them instrumentally. Darwin said that among species there is no higher or lower, which idea challenges anthropocentric assumptions.
One more comment, returning to science. See the book by James Rachels, "Created from Animals: The Moral Implications of Darwinism" (Oxford University Press, 1990). Ethics based on science. It explores how Darwin's theory of evolution shatters traditional ideas of human exceptionalism and argues that our treatment of nonhuman animals must radically change." And it seems that with lab meat, plant-based meat products (though still too pricey), and non-animal models for laboratories, scientists and engineers have provided a pathway for humanity to move in this more humane direction. It may also prove less costly, which is when you will really see things across industries change -- not for ethics but to save money.
I do not wish to judge anyone. We are all at different stages of understanding. I know some vegans can be seen as judgemental or intolerant. It happens with every sort of activist movement. I would say I am more of a conservative than the typical animal rights person. I have developed a few slide shows on it, including for churches, illustrating Rev. Andrew Linzey's arguments for a Christian animal rights theology, which I find quite convincing. Not all Christians agree with this; in fact, most do not, and their views are the result of socially ingrained prejudice. I get that because it describes the first half of my life too. I am glad I became animal-conscious. I credit my dog, Baby, who is in Heaven, who loved me with all her heart, and this woke me up to the world of animals. I hope to meet her again one day in the Afterlife. These are my honest thoughts on a controversial and complicated topic.