Well, I certainly agree that all else being equal we ought not kill X if there's a doubt about whether X is a person or not, and I support building AIs in such a way that they also agreed with that.

But if for whatever reason I'm in a scenario where only one of X and Y can survive, and I believe X is a person and Y is not, and the AI says that Y is a person and X is not, and I'm the one who has to decide which of X and Y to destroy, then I need to decide whether I trust my own judgment more than the AI's judgment, or less.

And obviously that's going to depend on the particulars of X, Y, me, and the AI... but it's certainly possible that I might in that situation update my beliefs and destroy X instead of Y.

I don't think you got the main point of babyeaters : they don't eat their babies (or let them die) because they don't know how to do otherwise (by lacking the technological skill, or because of suboptimal economy), because they consider it to be the most ethical thing to do.

No sane human will tell you that killing children or letting starve is an ethical thing to do. Some will tell you it's an horrible thing that must be prevented and give to charity to avoid it, some will tell you it's sad but we can't do much. Some may even tell you it's sad but required due to our current technological level. But none will tell you it's a good thing, and that we shouldn't prevent it if we had a sure way to do it. No sane human would actually oppose an alien race offering to save from death all starving human children.