This part always bothered me. He smiled while his son was getting killed and finally snapped out of it after all his friends told him to get involved, but it was too late.

I remember discussing this with other kids a long time ago and they said it was okay because Goku wanted to see how strong he was. They kept going full NPC even back then, repeating that he wanted to see how strong he was when I told them Gohan could have died at any time.