As this manga goes on its more and more apparent that the World Government and its Marines are the main evil in the world of One Piece, this isn't to say the average marine is a bad person but that the organization as a whole is not good and does not promote peace but only FORCES submission.
It's also apparent that in the world of One Piece, 1 person CAN change the world. And here we have Whitebeard "The Strongest Man in the World" as he is called and with GOOD reason - with 1 punch he can make fissures in the air itself, he can destroy entire islands by lifting a finger, he can stop a flagship size ship without flinching after already had taken enough damage to kill a lesser man, his knowledge is at least on par with Sengoku who is the leader of the marines and he can use that knowledge to become a great commander.
Now what does this epic man do with his life? Does he expose the World Government for torture? for its role in Ohara or turning people into giants (which I doubt was voluntary)? How about when the WG try and stab out any chance of Gol D Roger having a offspring by committing infanticide on several islands that he had 'reportedly' been to? (not to mention the Nobles owning sex slaves and things that may had happened that the manga hasn't said anything about).
No he does none of that, instead he just wants a family, instead of doing the normal thing and finding a wife (which if he just did that I'd understand - but he becomes a world figure) - he becomes a pirate captain, not just a normal pirate captain but the strongest one with many many allies with REAL possibilities. He dies a old man, while failing to save 1 person... that to me is a wasted life.