Do you ever just think about that the reason Goku was prone to violent outbursts and destruction when Grandpa Gohan first found him was because he was in an unknown place without either of his parents and had no idea why? And then theres this random old man hes never seen before trying to help him but all Goku wants is the people he watched from the nursing capsule for months.
Everything was different, everything was wrong. And so when he hits his head and forgets everything about planet vegeta and his family, the violence disappears. Because he no longer remembers what he lost...