When it comes to ideals, Naruto's are black and white because he thinks the world's only Yin and Yang, in a sense; you're either a redeemable good[
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] or an irredeemable bad.[
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] His ideals are somewhat parasitic as well - if he senses Yang in you, then he will TnJ you until you eventually think in his Yang-based ways, resulting in you doing what, deep down, he wants you to do.[
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] In Black Zetsu's case, Naruto has apparently deemed him an irredeemable bad.[
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]
Naruto's just like Hagoromo, believing in his own form of peace, not willing to even remotely consider anyone else's form of peace,[
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][
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][
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] and shoving his own Yang-based ways down your throat with the casual TnJ.[
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]
Gray you say? Look at the evidence I've linked to you; he doesn't even remotely try to think to himself "Could this work? Could this indeed bring peace to the world?" In short: He's a closed-/one-track-minded Yangtard who is not even remotely gray; the opinions of others can kick rocks for all he cares.
Now, I'm not just going to explain how Naruto is black and white and not explain how Sasuke is gray. Explaining how the latter is gray will be easy; for one, the author already admitted to him being gray, or rather "pure", in his ideals and views.[
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Unlike Naruto, who TnJs individuals with his parasitic views, Sasuke
was "TnJ'd" (in a way) by Hashirama.[
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] By learning what he learned from Hashirama, with his gray-/pure-mindedness, he was able to change his views and goals and went from wanting to crush Konoha out of blind revenge and nothing more[
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] to wanting to become Hokage and change Konoha's antiquated system;[
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][
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] if that's not gray, I don't know what is.
Just to add onto what should be clear now, Sasuke isn't afraid to 'tell it like it is' either.[
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]
Naruto, on the other hand, is either (1) afraid to do so or (2) so deluded in his Yang-based ways that he actually thought, in that instance, that Sakura and Kakashi were still relevant.[
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]
Side note: You know who else was thought to be good and innocent in their intentions and mindset? - Johan Liebert of Monster, who turned out to be a highly intelligent, sociopathic serial killer who had god-tier TnJ skills...