This is a bit of a fair point. I guess I'd have written the hypothetical in a few stages to address the underlying issue, which is presumably is either:

1) what happens if it turns out humans don't have compatible values?

2) How does our morality handle aliens or transhumans with unique moralities? What if they are almost identical to our own?

I don't think the babyeater story provided an answer (and I don't have one now) but I felt like it addressed the issue in an emotionally salient way that wasn't deceptive.