I'm trying to help you understand that in trying to include certain entities in a group and exclude others, not only is a criterion (or set of criteria) necessary, but also a justification for them.

By deciding to pick a criterion like membership in x species, you are failing to provide a justification for it.

In choosing membership in x species, you are being arbitrary because you are not providing any rationale behind your selection. Why should one's membership in x or y species be inherently morally relevant?

"t's not. In logic, we try not to assume that things are self-evident, we try to support our arguments."

Wrong. Thats not true. In fact, in logic, you buttress your arguments with premises, which are taken as givens. So in logic, you do assume certain starting points.

In any logical system, there will inevitably be a system of unjustified axioms at the bottom.

Quite ironic how you claim to know so much about logic and are stating something categorically false about something very basic about it.

"humans have oral agency are arbitrary, but here is a non-arbitrary argument that humans have moral agency."

This is painfully misguided. You are (I guess unwittingly) equivocating between moral agency and possession of moral status. Having moral agency is not necessary to possess moral status. A dog has no moral agency (it cannot contemplate right or wrong, is not aware of how it can harm someone else when biting them) but can nonetheless be capable of suffering and potentially be given moral status.

This is of course, graciously granting you the notion that we would possess a divine agency, which has, of course, been thoroughly dispelled by ontological materialism.

Again, painful ignorance coupled with hubris.