First dragon he killed by accident, second one he killed before he realized dragons could talk when it was attacking him, and the third was killed by the princess when it was attacking. Also after every dragon kill he's complained about having to clean up the corpse, so yeah his reasoning here is consistentHe killed 3 dragons for being to loud, can't kill dragon that destroyed his property and almost killed sakura? At least give MC reason why he can't kill her... I guess.. I expected too much from this manga.