There is one risk the author runs in omniscient point of view and that is that the reader, knowing what the characters think can respond more accurately than merely providing their own justification or guesswork as to motivation.
By what Updike gives the reader as to Rabbit's movements, his decisions, his reactions, one can choose to understand and either self-righteously blame Rabbit, denouncing him as a first class jackass or one can understand his frustration and sympathize, denouncing his actions rather than Rabbit's character. But once we're allowed inside Rabbit's head--or any of the other characters, in particular, Janice or Ruth--those thoughts will enhance our vision and clarify motive.
In other words, Rabbit is a real jerk. He's self-centered, immature, and while I can sympathize with his growing unrest and his weakness in seeking escape, I still think he needs a good slap on the side of the head. He himself seems to recognize that everyone is bending over backward to help him out and overlook his myopic introspection. Rabbit doesn't learn. His confrontation with Ruth and his treatment of her is forgotten immediately when he, that same night, runs off to be with his wife. He's "doing the right thing," even while making excuses that Janice is dumb and can't have the baby without him there. Within hours he's proclaiming his love for Janice, and it's not the sight of baby Rebecca that does it.
When the baby drowns, he's more concerned with how others will treat him than about his wife, son, or dead child. This is where, if Updike had shown Rabbit's actions alone, we may have supported him in answering his responsibilities, regardless of his unsteady emotions. But as we follow his thought pattern, we see he does what's best for him, even while blaming society for making him do what he needs to do.
This is character depiction at its best--and I suppose, its worst. We can understand Rabbit's disgust with Janice's drinking; but we get to see as well her reasons, her feelings and the insecurities and unhappiness that drives it. We might have been okay with Rabbit's treatment of Ruth had we seen only her tough, flippant exterior and the knowledge that she's a whore. Once we see her point of view, her fears and needs, her secrets, there is certainly more concern for her than what we might otherwise have had based on Harry's or the narrator's opinions only.