I thought I'd point out, in glorious detail, why Itachi fans are the way they are.
Manga
Before Kakashi knew about the Mangekyō, he said Itachi wasn't even giving it 50% of his
13 year old skills
(viz trans)
Meaning 13 year old Itachi was even faster and sharper with his base skills than those Kakashi "couldn't follow.."
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At the time, Itachi believed only another living Uchiha could
possibly defeat him.
(That is, only Obito truly had a chance in Itachi's mind.)
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After bringing Jiriaya to a cold sweat, and Kisame wonders why Itachi pretended like he couldn't solo.
SPOILERS: He was a good guy.
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Orochimaru knows that it's impossible for him to ever
(note: "dream/aspiration") defeat Itachi.
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A 7 year old Sasuke
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was still behind Itachi in development.
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Itachi at age 7 didn't even have to be taught
(and some trans say he was the greatest genius of the academy
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.)
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He awoke and mastered the Sharingan in one year.
(It took Sasuke three to five years, and Kakashi around fourteen.)
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Even if Orochimaru had Kage-level help, it would be impossible to defeat Itachi.
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Oh, Sasuke, you can defeat countless ninja
(my entire country) easily? That ain't SHIT to Itachi, son.
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An
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Itachi made Orochimaru feel hopeless.
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Itachi defeated (multiple) S-rank Akatsuki easily.
And looks like a god while doing it.
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Itachi's
clone defeated the main character easily
(err, again.)
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Itachi was so weakened against
(the Kage level) Sasuke that Zetsu thought he'd been severely injured beforehand.
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Itachi found ancient artifacts of immense power that not even Orochimaru or Madara could.
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Madara's wisdom believed Itachi was completely invincible.
and based on how (Gin's bankai!) it handled Orochimaru/Nagato in between panels: why not?
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The Yata Mirror (stated to flawlessly turn back any attack) is also stated/shown to morph shape.
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Blind and near death, Itachi sealed Orochimaru
(RIGHT after he powered up and finally took over Sasuke lol.)
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Obito said that Itachi never ceased to amaze him. That is, he amazed the main villain ALL THE TIME.
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Obito said Itachi was the only one to see right through his stealth
(virtually all others have failed at this.)
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Obito didn't know how Itachi did his fūindōjutsu trap.
(Let alone surgically implanting a Mangekyō into an ordinary crow and having it use it despite obvious chakra-supply/non-Uchiha engineering problems.)
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Obito said he made damn sure to keep secrets
(i.e. stay away from) from Itachi, or else he'd certainly be dead.
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Obito says that Itachi was the sole person that impeded his vendetta against Konoha all those years.
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Itachi was such a beast with genjutsu that he was compared to Heaven above earth.
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Danzō said that Itachi only ever made one mistake
(loving his bro too much.) 
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Shikaku
(who knew Itachi. Ao didn't.) believed Itachi could literally genjutsu-control an army.
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Itachi also believed that his (unknown) illusion powers could affect the war on a large scale.
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Kabuto said he's on another level.
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Similar to the beefed up Orochimaru, another beefed up past main antagonist is abruptly sealed.
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Kabuto said Itachi was just too damn good. With basic skills.
And he deciphered/countered Rinnegan vision much faster than any other genius.
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Itachi knows every jutsu has a weakness
(and with his intelligence hype, he'll find it, so he's the weakness!)
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Kabuto considered Itachi a completely different beast (a higher caliber genius) to any other Uchiha.
Kabuto, being the "greatest genius of lying," is one of the only dudes who could counter Itachi's mind-reading in battle.
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Kabuto believed that nobody
(not Madara, not Hashirama, nobody) was more worthy of being his Edo Tensei than Itachi.
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So
three main antagonists of the manga were finished off by Itachi.
That's more than Naruto and Sasuke combined.
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Sasuke said Itachi was perfect.
(Itachi said he wasn't perfect. But modesty only counts when it's Hashirama. )
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Itachi ultimately improvised Kotoamatsukami to save Naruto/Bee
and set Sasuke/Kabuto on the path to redemption.
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Itachi was as wise as a Hokage
(Hiruzen was saying this, so as wise as Hiruzen?) at the age of seven.
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Hashirama considered Itachi a better shinobi than himself.
The god of shinobi praising the uber god of shinobi, if you will.
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Databook:
Only those on his level can even fathom his potential.
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Symbolism
Feats (why Itachi can logically defeat
almost anybody)
Itachi's shunshin and clone feints are too fast/sneaky for top tier reflexes/sensing to track.
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Essentially, it was the same late-warning that Deidara needed against Sasuke
(then Deidara went to long range.)
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The only other move to get the drop on Bee like this was Hiraishin.
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Bee even countered the bloodlusted Raikage.
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Clone feints use shunshin jutsu:
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Itachi has formed clones and flicker away so fast that perfect Sages or Sharingans don't notice.
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He's also blitzed
multiple Sharingan users and knicked Kabuto (something Sasuke's Susano'o arrow didn't.)
The Susano'o arrow's movement being so fast that Kakashi couldn't physically dodge.
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Itachi's countered perfect Sages, unlike Raikages:
This is also a strength-testament, and it's further backed by Itachi blocking Jinchūriki.
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He moves so fast that even Naruto/Bee were stuck in their position when he moved back.
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So imagine those clone feints or flickers being combined with the speed of his jutsu:
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Especially when, in almost all cases, you're not allowed to really look at him (Tsukuyomi, finger jutsu, etc.)
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So, that's why there are so many fans. He's basically prime Hiruzen
with the Mangekyō
and in-battle mindreading & invincible artifacts.
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(Convert! Convert! Convert!)
