he joined akatsuki because he knew madara is alive and he have a haunch that madara would be destroying konoha, since originally madara wants to destroy konoha since he feels that their clan was used by the first hokage,maybe because of the uchiha pride.... then he made a deal i think with madara not to harm konoha,.... then madara on the other hand,madara knowing itachi's whole secret, maybe thinks that sasuke would be of better use than him, waited until the day the itachi would die and manipulated sasuke to be his tool to totally destroy konoha, ... but the transferred powers from itachi also became sasuke's protection against madara.....
generally itachi was just a very loving brother and the martyr hero of konoha.... and a genius for sure......... i dunno if a make sense, correct me if im wrong with my opinions....
