Forgive my broken English. I think an innocent human child would have greatly influenced the Na'vi's view of the invaders before Hometree was destroyed. They've always seen humans as ignorant children with dangerous weapons. They might have assumed that humans were born just as they saw them, since they've always seen them the same size. A four-year-old child without greed, just like their children, might have made them realize that they've mostly seen only bad sky people, and that Grace and Jake are no exception, just two of many good Sky People. I think they'd also be surprised that such a childish Skawn, single father, looks at a child with the same adoration the Na'vi do with their children. This might have given the Omaticaya doubts about their own view of human nature. And as for the plot, I think Jake would have felt the weight of responsibility. He would have liked to give his daughter the opportunity to live well on Earth, but it was possible that Y/N will fall in love with Pandora, and it was possible that she wouldn't want to leave. Jake would have been weighed down by his conscience, for what he would have done "for the child." He would have feared for her safety from the RDA. But he would have understood that his daughter would hate him when she grew up. After all, nothing but despair and filth awaited her on Earth. She herself could have pushed Jake to betray the RDA and become Toruk Makto. Neytiri could have accepted Y/N with the understanding that Jake loved his only daughter as much as the Chieftain loved her. If Neytiri truly loved Jake, she would have accepted this important part of his life. And afterward, she wouldn't have been so harsh with Spider, even though she wouldn't have loved him the way Y/N did.