>>536510429
Something I don't see highlighted often enough is that the Freeza fight is possibly one of the worst times in Goku's life. He's losing himself to rage for the first time, he's got the "evil" speech bubbles because of that. The shift is huge and he's losing his innocence. At the end of the fight he tries to regain control by letting Freeza go and reverting to base (with the round speech bubbles again) but Freeza backstabs him with the first Kienzan, forcing him to revert into the Super Saiyan state

Despite Goku's best attempts he had to go all the way and become a heartless warrior, fighting on a dying planet just because he hated his opponent so much, refusing to teleport back to Earth. It took a toll on him