Itachi's too strong to sit around Konoha and do nothing. I believe he was destined to leave Konoha and seek the missing piece to his puzzled mind. Itachi is indeed searching for something, possibly on a quest to find his trueself. <~ Just my opinion. Itachi wouldn't be able to stay quiet and live a normal life, because he has too much powers to keep it unused. ANBU is all about assassinating, killing, etc...and he became bored of that obviously...so what else is there left to do? He has no heart of a Hokage to sit around and protect the village, so I believe it was IMPOSSIBLE for Itachi stay in Konoha.