I'm doing my best not to commit these fallacies, though of course not claiming to be infallible.

I mean, we know a fair bit about what causes pain for humans in the physiological/neurological sense -- we know about nociceptors and how they work -- and we also know what kinds of behavior we expect to see when a human is in pain. We also know that mammals have the same kinds of physiological mechanisms that humans do for pain, and we know they respond to injury with the same kinds of external behavior that humans do when injured.

(All this could not be said of plants, computers, or even quite likely non-vertebrate animals (although I do err on the side of caution with those and don't eat them either).)

So, yes, I am claiming that there is a lot of evidence that pain and suffering for non-human mammals is a similar kind of thing to the pain and suffering that humans experience. And I am suggesting that when we cannot possibly know another being's subjective experience as if from the inside, but everything we do know about that experience (the neurology and the behavior) is consistent with it being the kind of thing we would normally hold ourselves ethically obligated to avoid, then we are ethically obligated to avoid it.