Coribn117, that is not how the human brain works at all. Would you consider someone who has polaroid memory to be insane? They remember EVERYTHING that they see. Perfectly. Sigmund Freud had that... (1 in a million chance of being that.) He also remembered everything that anyone ever SAID. Perfect auditory memory. (Also is 1 in a million chance. This means Freud was one in a trillion.)
The human brain can be argued to have infinite amounts of space for memory. In fact, it is highly debated that the subconscious (if it REALLY exists) remembers every little thing, the concious part of the brain just cannot recall it. Plus, within twenty seconds of learning / hearing / seeing something, the human brain decides whether or not it should put it in permastore or forget it. And things in permastore are NOT forgotten over time, they just become harder to recall. It is just like a computer needing to defragment.
Also, the sharingan doesn't exactly work the way you said it does with memory... That'd be impossible. You can copy and instantly have perfected any genjutsu, taijutsu, and ninjutsu... But the ability to perform it is different. I know EXACTLY how juggling works and how to do it. I still can't. The sharingan (because Naruto is a fictional work) makes it so that you can instantly perform something as well.
Itatchi is just pretty much an asshole who was brought up poorly and felt that because he could out perform everyone, he needs to do such and such. He has antisocial personality disorder. Sasuke doesn't. He still feels regret and still feels emotions. The problem with Sasuke is that he was scared for life by the horrible deeds of his brother. He is overwhelmed by his obsession and pretty much just wants to do the deed of killing his brother. It is almost as if he has an odd form of OCD. It interferes with his life and etc.
Nam Myōhō Renge Kyō[/CENTER]