I think Aaron is the Aaron we know. Otherwise the storyline of "you can't let anyone else raise this baby" goes nowhere.

But an alternate theory I'm considering is that the baby is Sun's(!). We know it's not Jin's baby. She is assuming it's the rich guy's. But maybe the baby was conceived on the island as a result of the Others' experiments. Sun gives the baby away rather than tell Jin that their baby was white. (too complicated!) Hmm... that would mean that Juliette is still experimenting...

But the baby is Jin's. And the rich guy that she had an affair with wasn't white anyway. He was Korean, too. But I agree with you on the "don't let anyone else raise the baby" thing. It seems like that was all too important to ignore considering someone else does, in fact, end up raising the baby. Which leads me to believe that the psychic foresaw something bad that would happen had someone other than Claire raised Aaron etc, and because of determinism, which is a huge theme on the show, the universe course corrected itself once again and not even a plane crash and island marooning could stop someone else from raising Aaron. Meaning the story of fate still continues.

Unless I missed something, I believe we can't know that Sun's baby is Jin's. The baby was conceived before they crashed. Jin is supposedly infertile. By "island miracle" it could be Jin's. But I think we don't know. We are also led to believe the father could be the rich Korean man she slept with.

But some of the key information here was given by Juliette at a time when she was clearly still answering to Ben. Sun may be part of an experiment. And the baby may be Ben's for all we know, and if it is implanted, it may not even "really" be Sun's.

If the baby is an "Other", that could explain Jack's reluctance to see it. It would be a huge reminder of Juliette's betrayal. Thus the comment from Kate something like if Jack can't get over what the baby represents to him, then "there is no you and me." In other words, if he can't get over Juliette, there's no Kate.

Is it possible that the baby is a girl named "Erin"?

"After Juliet migrates to the camp, Sun demands to know about pregnancy on the island, and is shocked to learn that women die during pregnancy. Juliet takes Sun to the Staff station, where she uses the medical equipment to determine a date of conception; Sun learns that she conceived on the island, making Jin the father, but leaving Sun with less than two months to live before her second trimester." (info from wikipedia)

I don't think that they would put that in there as info if it weren't in fact true that the baby was his, I think they would put that "most likely" or whatever. When there have been direct misleads before they've always said something.
But you're right! Anything can happen.
I misread your post, I see know that you are pointing to the fact that Juliet could have been lying. My bad.

oh, and I don't think that it's possible that its a girl because Kate says in FF "my son" and she says to Jack "why you wouldn't want to see him" I could see her lying to protect the baby's identity to the lawyer but not to Jack.

This theory is about to be proven FALSE. Wait for it.... NOW!

On the super special extended edition with extra spectacular deleted scenes there is a scene were Kate is in the locker room trying to get her cuff off. Its pretty brutal and she hurts herself pretty bad. Thats what happened...Wal-Mart sold a special edition that came with 2 extra deleted scenes. The other one was Sawyer finding a gumball in a Dharma cereal box.

How two non-Caucasian parents are to come up with a blond child is beyond me.
How Sun would give away a child she & Jin longed for is another mystery, let alone the speculation that she would pull this off without letting Jin see the baby.
Occam's razor: "entia non sunt multiplicanda praeter necessitatem" or as in English "entities should not be multiplied beyond necessity".

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"Bear...? Is that you?"-- Hurley S03E4

Ok, you almost have me convinced that it's not Ben's baby - mostly because of the deleted scene with Kate struggling to get the chains off. But I'm still not convinced it's Claries "Aaron."
Kate and Sawyer are going at it like rabbits and I don't think there are a bunch of condoms on the island.... do you think it could be Sawyers kid? I could see Jack not wanting to see that "love child."

Ben is a murderer but not rapist

this seems not in keeping with the spirit of LOST and my bet this would really turn off viewers

yeah, ben is a murderer and a very good liar..... but has too much class to be a rapist.