If you simply claimed that you’re against pointless killing I wouldn’t consider that arbitrary, since I share your strong intuition that causing meaningless suffering is deeply wrong. That is, in fact, precisely why I find it confusing that you would violate this intuition.
And that is where you will find your answer, I have a personal intuition both about what lives I value- I don’t believe all pointless killing is bad, regardless of life form, I don’t care if someone pulls up the plants in their yard because they feel like it. And you clearly value some life less than human life given that you eat to exist.
An arbitrary moral distinction would be like claiming that you are against ending innocent lives, unless they’re a different race, gender, species, nationality, or color than you, given that none of these factors have any moral relevance.
What? You understand an intuitive belief can exist for all of those things right?
What is the moral significance of a creature’s nationality or species?
Pretty obvious, I care about the lives of some species and not others. (Do you take antibiotics?). It is based on some framework, that is ultimately based on intuition as well.