Ok this is just pure spculation and lack of sleep. In fact don't even read it, cause I'm just getting crap off my chest.
Kohona ninjas are taught first and foremost that as ninjas they are to protect the village and its inhabitants. Itachi graduated when he was 6 years old. It was his extreme talent that allowed him to propel into the ranks of ANBU quickly. I think it was his extreme talent at such a young age that destroyed him. A prodigy grows up basically thinking he is alone, and being an ANBU member, Itachi has probably seen by now hundreds of deaths, and possibly even committed hundreds of them himself. Somewhere along the way he feels that theres no point in protecting people, when they can be killed so easily, and its easier to be a ninja if theres nothing you need to protect but yourself. So what does Itachi do? Kills the lot of his clan so he doesn't have to protect them.
