I won't say whether I think he is a hero or not, but it is obvious that in the Narutoverse he is portrayed as a hero. Naruto is not reality, so Kishimoto must think he is a hero. A hero in Naruto might not be considered a hero in reality. So then you must just disagree with Kishimoto, which is ok. This is just like how some people think Sasuke's revenge is good, and others don't.
But according to the manga (not reality): It does not seem like any killing could have been avoided because even when Itachi was right there in front of his father, his father still said that they think differently, which hints that his father (the leader) was not going to change.
But I'm just saying that it seems like in the Narutoverse that Itachi is portrayed as a humble hero. If someone does not think he is a hero, then I guess they disagree with Kishimoto. It's ok if you have a different view though.
It is obvious to see that Itachi is one of the more loyal, caring, loving characters. And even if he didn't always do things the best way, he still had good intentions for the village. And if you think that he did not care about his clan, well if he did not do what he did, then according to Danzo, Sasuke and Itachi would have died along with the clan. So it's understandable if someone disagrees with some of his actions, but it is shown that he wanted to protect Konoha, his brother, and have his brother bring back honor to his clan and restore it. So according to the manga, Danzo might have tricked Itachi into thinking that talking with the clan would not work. Danzo might have killed Itachi and Sasuke, I don't know. It was like Itachi said to Danzo in the one page, "Are you threatening?" And again, if you compare Naruto to reality, then very few characters are heroes, if any at all.