[nefitty]

It's not at all arbitrary. My starting position is that I want to be free of pain/suffering and I want to be able to pursue my desires and preferences. I take those as inherently good. I apply those internal truths to other living beings.

Plants, bacteria, etc don't feel pain, although they might have preferences for food, etc. Those beings, then, are not especially relevant to our ethical obligations viz a viz the experience of suffering.

A fish feels pain and exhibits distinct preferences. Therefore, we are obligated to respect its life by virtue of the inherent good of painlessness and autonomy. It is immoral to kill any living creature that fits that framework.

Finally, this does not mean that our moral obligations are cemented here. We may eventually learn that other living things have properties that require us to expand the scope of our ethical duties.

[c22]

It sounds like your moral framework would include bugs as sacrosanct as well? I do wonder, then, why you are so quick to dismiss the feelings of plants? I guess because they move in time-steps out of sync with your own? But if you take a shade-loving plant and put it in the direct sun it will turn its leaves away so they don't get burnt. If you stab a tree it will exude a coagulating sap and heal the damage with a scar. Plants have no immune system comparable to ours, but they still remember and respond differently to viruses they've been exposed to in the past. These actions are clearly in response to the environment. Since my own pain-avoidance and healing actions are very similar and also in response to the environment I consider this evidence that a chemical analog of my pain response must be occurring in plants, however alien the experience may be to me as a mammal. Whatever plants feel, there are other moral issues surrounding the food chain that cannot be solved by simply adopting a plant-based diet. I think it is more arbitrary than you are willing to imply.