Itachi is probably the most controversial character in the Narutoverse, beating the excessive positivity of Minato, the dubious choices of Sasuke, the neverending rivalry between fans of Sakura and Hinata. There's just nobody, as far as I have seen, who invokes discussion more than Itachi.
Yet most fans and haters of Itachi agree on his fundamental aspect, which is the baseline for both praises and insults to Itachi - and that is, the notion that Itachi is the "perfect" character of the Narutoverse. Itachi is strong, resourceful, smart, wise, cunning, righteous, altruistic, loving, caring, selfless; whatever opponent Itachi faces, he "soloes" him, whatever choice Itachi makes is the right one, whatever thing Itachi says is correct, whatever evil act Itachi commits, it is always justified by a way greater good.
Itachi is supposedly how Kishimoto envisions the perfect ninja (= the perfect soldier). It is intended to look perfect by the author willful decision. He is the epitome of never-failing coolness as envisioned by Masashi Kishimoto.
Ironically, both fans and haters usually share this belief.
There is, however, an important person who begs to differ - and that person is none other than Itachi.
Itachi openly states again and again that the mass murder he helped carry out is an unforgivable sin. He speaks of himself as someone who lost sight of his own identity by playing the triple-agent for many years and as someone who lost the ability to trust others and thought that he could manage everything on his own - this reveals that the anger and frustration Itachi expressed in the first flashback of Sasuke's was genuine, and the feel of loneliness and despair by being separed by his own clan were sincere. He openly admits being guilty of Sasuke's turn to evil and confesses that he always tried to manipulate others, going as far as mentally torturing Sasuke in life and try to brainwash him even after death either by silencing the witness (the Amaterasu he sealed in Sasuke's eye to kill Obito) or by altering directly Sasuke's mind (the Kotoamatsukami he sealed in Naruto), which is a direct consequence of his excessive confidence in himself and his scarce confidence in everyone else. Also, his reasons weren't entirely for Sasuke's good, as he once again confesses: he hoped that Sasuke would kill him, cleansing him of his guilt and restoring his clan's name.
All these things aren't speculated or hypothized - they are stated explicitly in the manga, by the most credible source: Itachi himself.
Maybe people would stop idolizing him as a god or, conversely, despising him as a flat character with no flaws, if they paid more attention at the manga and finally accept Itachi as a good character, with downfalls and flaws as every good character should have.
