Watching this Debate on Extinctions, I was struck by the fact that the assembled panel seemed to have no clear consensus on the morality of recreating Neanderthals, even though most of them seemed to be in no doubt that this would be at least technically feasible within a matter of decades.
That video is the second half of a fairly long debate, so I'll just summarize a couple of points I think are now generally accepted by researchers, as background to the ethical issue...
1: Neanderthals had very limited language capabilities (they lacked the anatomy for versatile vocalization, the brain areas concerned with symbol processing are underdeveloped, etc.).
2: It looks like Homo Sapiens didn't just "outcompete" Neanderthals for resources - our ancestors systematically exterminated all other hominids they encountered. Which wasn't too difficult, since "we" could devise, communicate and refine plans for a better future, which other hominids couldn't.
I reason from the above "facts" that if we did recreate Neanderthals, our ability to communicate with them would forever be on a par with how we interact with, say, cats and dogs - they don't and never could have anything like human self-awareness, or a concept of "the meaning of [their] existence".
I don't want to get bogged down in whether those "facts" are irrefutably established in the specific case of Neanderthals - if not them, there will surely be other even more primitive hominids we could eventually recreate, who would most definitely lack those mental capabilities we define today as "quintessentially human".
I'm also completely uninterested in the religious perspective here. I think religion and morality are at best orthogonal, and only "secular" morality can be expected to prevail in the long run.
Finally, I don't think the morality of recreating Neanderthals strongly correlates with the morality of creating self-aware Artificial Intelligence (which may or may not be technically possible), since in that case by definition our "unnatural creation" would be able to discuss their circumstances with us, as rational thinking entities. In essence, what I want to focus on is...
Exactly why might it be "immoral" to (re)create a relatively intelligent but not self-aware humanoid biped (complete with opposable thumbs, etc., and all that implies)?
EDIT: To keep things tightly constrained, I want to address this issue in terms of Utilitarianism. I can easily find texts exploring the ethical treatment of existing animals from that perspective, but I'm specifically interested in the ethics of (re)creating a "non-self-aware, but intelligent" animal.