Luke's on a quest to follow in his father's footsteps, one which he had been blocked from pursuing by his uncle.
Even so, he rushed home into danger to try to save his aunt and uncle. Instead of curling up into a ball upon finding their remains, Luke was filled with determination to set out on the quest he had always dreamed of. Keep in mind, Luke also realizes that he is now marked for death by the Empire, like his aunt and uncle.
Luke's choices seem to follow plausibly from clear motivations of his character, not only on their own merits but especially in the context of the fantasy genre.