Some of his moronic-ness is because kishi wants to educate the readers about like the nuances of the naruverse. Because we dunno the in's and out's that the avg shinobi would learn in ninja academy, he had to make naruto seem like an idiot at times so he could explain to the reader how shizz worked.
One example is when kakashi and yamato were teaching him about nature manipulation. you'd think they'd teach that at the friggin' ninja academy coz that's SORTA important. and they prolly do, but he makes naruto seem stupid so he can explain it to us. Otherwise, naruto has his moments of brilliance.
As far as him not knowing, its the same thing...it has to be done in order for the story to flow. Kishi writes this manga with a specific idea in mind about how he wants his character's personality to be...if naruto had known that he was the 4th's son, i think it's safe to say he would've been COMPLETELY different, and this might be different from what kishi was aiming for. Also, it saves the opportunity to have a strong, emotional moment. I'm thinking someone important, like Tsunade, will let him know after he succeeds (which he undoubtedly will) to bring like this awesome emotional scene and justs adds to the epic moment, ya dig?
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