Okay, but even leaving aside the pain stuff, people generally find subjectivity / consciousness to have inherent value, and by extent are sad if a person dies even if they didn't (subjectively) suffer.

I would not personally consider the death of a sentient being with decades of experiences a neutral event, even if the being had been programmed to not have a capacity for suffering.

I think the idea of there being a difference between an ant dying (or "disapearing" if that's less loaded) vs a duck dying makes sense to most people (and is broadly shared) even if they don't have a completely fleshed out system of when something gets moral consideration.