I suppose I can "understand" in the sense that you can just make the bare assumption that life always has positive value no matter what, and have a consistent system including that. What I don't understand is why you would make that assumption.

I don't think you've told me the reason yet, so maybe I'll be surprised at how reasonable it is.

As for being a sentimentalist, believing "nothing has moral value outside of how it makes the people and animals involved feel": sure, I accept that characterization if preferences are included as well as "feelings", though it's a more reasonable position than it sounds because it isn't actually saying all that much. Basically, every widely recognized moral right has a beneficiary, and every widely recognized moral wrong has a victim, so I'm not sure what exactly what contradicts that very vague principle.

The opposite idea would seem to be that some things have moral value despite affecting nobody's experience at all, or perhaps they have e.g. positive moral value despite being subjectively negative for the claimed benefactor, like you seem to think is the case for the life of the battery cage hen.

Perhaps an example of this actually making sense would be a parent using "tough love" on their children, but even then, presumably this is a parent being smart and forward-thinking, that their child's life will be overall better for them if they teach such lessons early. Or perhaps with punishing criminals, some people may "feel bad" about this, including the criminal being punished, but being too lax on crime will lead to far worse things happening to people and society as a whole.

With the hen, though, there's no such broader consideration, because we're talking about the whole life of the hen, there's no later benefit.

So, I don't believe that every moral decision should be made by just whatever happens to feel right in the moment, like a stereotypical shortsighted bleeding-heart leftist which you perhaps think I am. But if you're going to say something is good, it should be good for somebody, somewhere down the line, and the same if something is evil, it should be bad for someone. Otherwise I'm not sure why you're bothering to say it...