Regardless of pain perception: Assuming someone is okay with killing a fruit fly but not a human, they have to draw the line somewhere. And a pig for example is WAY closer to human than to a fruit fly. It's a sentient being with a brain that's not really so far from human, compared to the fruit fly which is essentially a tiny biological robot.

In fact, it's kinda weird to draw the line at humans, especially when there's such a big overlap between other animals and human children in terms of cognitive capabilities.

I think it's very reasonable to draw the line after insects, where we can be reasonably certain that there's no complex thought or sentience. The value and subjective experience of an insect versus a farm animal are hardly comparable.

This is something I think about from time to time and essentially get nowhere.

I try and live-capture and release bugs from my house (the only things I actively kill in this regard is mosquitos).I also hunt/fish.

If I saw a deer trapped on a frozen lake I'd go out and rescue it, yet I'd shoot that same deer in a different place under a different context. It's not really consistent, except in intentionality I suppose.

I do place a higher value on the life of animals that are more "intelligent" (in a way that feels more human) compared to other animals. For example, I'm not upset at all when I use hand sanitizer and presumably wipe out a whole swath of life, but I'm sad if a bird hits a window and dies. Part of that is the intentionality again maybe? The bacteria "had" to die, and the bird didn't; I'd feel less bad about the bird if I saw a natural predator take it down but it's still more upsetting than even unintentionally killing an insect.

I'm not vegan, I'm just trying to eat less meat, but I see this discourse pop up from time to time in vegan communities.

A similar argument is often made regarding what would happen to vegetarians if they learned that plants can feel pain. This is often posed as a hypothetical, but I've heard that some studies suggests plants and fungi especially may be aware of when they're being eaten. Whether or not that equates to pain, I don't think a consensus has been reached.

But for the sake of argument, let's say that plants do feel pain while you eat them. If your ethos is to reduce overall suffering in the food chain, then it's still logical to abstain from meat. Livestock living a vegetarian life eat a lot of plants.

You might alternatively come to the conclusion that there is no such thing as ethical consumption. An extreme position you might take is that the best way to reduce suffering is to remove yourself from the food chain. If you starve yourself, you'll be consuming less, your greenhouse emissions become zero, and you lessen your impact on social services and infrastructure that is often strained to the breaking point.

Obviously, the solution is not to just kill yourself. But advocating for more ethical consumption seems like a noble cause.

For that matter while just walking around you will be killing bugs like ants and spiders by stepping on them. Just by taking a shower you will kill microorganisms that live on your body.