yes i realize that he can have simple motives however you gave an horrible example Itachi isnt some obedient dog who does whatever he is told to by his superiors so he wouldnt "simply" take the orders of anyone in less their motives paralleled his own
that does not sound really all that "simple"

my point is that a good story teller gives his characters depth and i think that we would all agree that Naruto has some great story telling
if you want to understand itachi then you have to look at him as more than just a "psycho" or "not a psycho" type of guy

even the simplist of actions have complex motivation