In all seriousness, I always just assumed that Oda had created the OP world (or the OPlanet, as I like to call it) as a storytelling vehicle for his characters to have these kinds of adventures.
EDIT: Uuurrrgh! Can't..maintain..seriousness!! Must..write..more..crap!
Marine A: Captain on the deck!
Captain T-Bone: At ease, men.
Mariejoan Soldier A: Captain T-Bone sir, begging your pardon…
T-Bone: (Turns, faces soldier that addressed him) Yes, what is it?
Soldier: (Thinking) {Scary!} Um, sir, we've heard many outlandish tales about these heathens, the Strawhat crew. The men and I were wondering…are they true?
T-Bone: So the rumors of their inexcusable conduct have even reached the Holy Land, to soil innocent ears. Oh, the shame!
Soldier A: Sir, we've been told that they sacrifice babies to some abomination with the body of a man and the head and hindquarters of a reindeer.
Soldier B: Sir, we've also heard that they kill any man that refuses to join them…
Soldier C: and that those that do join are castrated, and forced to serve as euneuchs to guard their captain's harem.
Marine A: {I knew they had done some outrageous things, but this is worse than ANYTHING I'd ever heard about them!!}
T-Bone: No, son. Those tales are as nothing to the pernicious truth that is the "Sin" called the Straw Hat Pirates. For they have done something so loathesome that not even god himself could forgive.
Soldiers A, B, C: Gasp
T-Bone: They wounded my men! Maimed them, to the point that they shall never again be able to sail the seas with their heads held high!! And without another thought for what they had done, they abandoned their victims to whatever fate the seas could conjure! Unable to sate their savage bloodlust with this abominable act, they turned their attentions toward the Island of Justice, the very symbol of all we strive to uphold, AND RAZED IT TO THE GROUND! But, to ensure that no one could find any good in them, they burnt the flag of our World Government. For these crimes, these sacreligious vermin must be exterminated from the earth! Oh, how my heart aches when I think of my men! Lying wounded and crippled in some foreign land, dismissed from service honorably, yes, but dismissed all the same!
T-Bone's Crew: {Why does he keep saying that when we're right here?}