I keep thinking about what the psychic told Claire before she got on Oceanic 815 - she said Claire had to raise the baby herself. She was going to give it up for adoption, right? Well, Claire ultimately abandoned her child which allowed Kate to "adopt" him and raise him off the island. According to the psychic, this is bad - so what would bringing Aaron back to the island do?
For one, it wouldn't allow Claire to get on a helicopter with the poor kid.
I forgot about that!!!! Did we actually see Desmond's vision in that episode?? Maybe it means that at some future point she will get on a helicopter with him. Of course, I am assuming that Desmond's vision would have been of Claire getting on the 'copter with baby Aaron as opposed to infant Aaron...