And they needed those pirates to keep balance. Would be interesting though to see the WG voiding the Shichibukai and having some kind of a reverse coup d'état.I know something like that wouldn't just happen right away nor did I write it would but if the Marines add the WG gather enough power it could happen, the Sichibukai are pirates after all
I'm pretty sure Oda knew that everyone would know after 731, it's not that he is hiding that it's Sabo, he's simply hiding his design until something awesome happens
Or he is making a mockery of Tobi/Obito and everything that surrounded his secret identity >.> Doubt that though