@jerkface@lemmy.ca can correct me if I'm off-base here, but I think what they've said can be simplified to "empathize with the animal." Addressing land mammals like cows, goats, and pigs, which I think are a gateway for a lot of people, you start with the premise that the animal is sentient – capable of happiness, fear, suffering, anger, excitement, love – and work from there. (Just to clarify, I think that "pain" is where the buck really stops, but sentience is a good bridge.) I think most people will acknowledge that dogs are fully capable of all of these things, and that it's wrong outside of very extenuating circumstances to hurt them (let alone for personal pleasure or gain). They have rich inner lives, they have fears, they have loves – they have a world, one that starts with them and ends with them.

Consider for a second that every person you'll ever meet has their own inner world that you'll never really know or fully understand. You can query them, sure, and humans have remarkable tools to communicate their worlds, but it's ultimately somewhere you'll never be. Wordlessly, though, I'm betting that you can assume those people have wants – to be safe, to be comfortable, to be happy, to be loved. Inside their world, what they want at a fundamental level is probably something like what you do. And I'm willing to bet that through empathy, you have some appreciation of and respect for that.

I fundamentally believe based both on the preponderance of the ever-expanding body of scientific evidence and on my own experiences interacting with animals that many of them have the same basic wants as we do too, and that these include animals like cows, goats, sheep, chickens, and pigs. I think a lot of people – myself previously included – simply fail to realize this because we're raised not to, because it's just alien enough, and because we have every incentive to keep feeling that way.

I think my first step into cutting out meat began with "if I were there in person, could I bring myself to kill this defenseless animal for food instead of just eating something else?" – because functionally I was doing the same thing by paying someone else to do it. And even as I began to process my feelings more and went from a typical omnivorous Western diet to pescetarian to vegetarian, I always found myself getting stuck on veganism. I was suddenly stuck back where I was when I was omnivorous, where in hindsight I was rationalizing my way out of empathy. I can't remember when it was, but at some point, I found my way from the vegetarian subreddit onto the vegan one after people would show up there condemning the cheese recipes as cruel. I began to lurk there out of curiosity, and it was basically inevitable – unbeknownst to me – that I would stumble across the 2018 factory farming documentary Dominion. Setting aside some time one evening, I started it...

It took multiple sittings across multiple weeks because I almost couldn't bear what I was seeing, and from that, something viscerally clicked inside of me: that we're, on purpose, giving an animal a world, only to make it one where their life is spent like this. (NSFL) One where every waking moment, the world they want and deserve just the same as we do is broken, worn down, drawn further away, and dangled in front of them as something they'll never have – stealing theirs for some ultimately superfluous part of our own. We've given them their one chance at life only to force them to spend it in agony. I realized at that point that the only arguments I ever made for myself that weren't predicated on outright falsehoods – i.e. not I can't be vegan; I would be less healthy vegan; they can't process feelings; nothing I do will impact anything – could all be reduced to "might makes right", and that to me was no way to live a life.

They're delving into the religious side of it in the reply to you. It is exactly like self delivering catholic guilt.