And now we have evidence to suggest that we were wrong, thus there is a moral imperative to act based off this new information. There is no evidence that bacteria or similar organisms are capable of pain or suffering. If you want to just disregard all science and biology, that’s your prerogative I suppose.
I don’t want to disregard science. I want to err by being preemptively more inclusive, not more cruel, when I don’t have sufficient information.
If you don’t have any evidentiary basis for your inclusiveness, then that makes it completely arbitrary. Why not start worrying about potential cruelty to non-living things like air, or rocks as well?
Because, as you say, they are non-living. What is and what isn’t life is not arbitrary. It’s a distinction based on science.