Why I don't hate James Potter
James Potter is not a particularly good man. Neither was J.K.R.'s dad. She wrote the books shortly after the death of her mother, and besides exploring death and loss, the books also explore the challenge of growing up and becoming disillusioned with one's parents.
James Potter is the analogue to J.K.R.'s father, who she had a difficult relationship with. After fleeing domestic abuse, J.K.R. decided to stay with her sister not her father.
Harry also has a difficult relationship with his father. He loses James as a baby, and then goes through the additional pain of losing respect for James as an adolescent. As a small child he has an unrealistically idealistic picture of his deceased father. But when Harry sees Snape's worst memory, he has to grow up and realize his father was deeply flawed.
Harry is ultimately able to reconcile the dark and light of his father. He realizes James is both a flawed human, and someone he wants to love and honor. That level of acceptance for a flawed parent is admirable, especially given that Harry has no memories and few stories of his Dad with which to make sense of the man's character and his feelings towards him.
James Potter, unlike Lily, is gray. So is Albus Dumbledore. So is Severus Snape. What I love about the HP series is that it is full of humans, not walking embodiments of moral ideals.