you guys are looking at what itachi is saying all wrong
he wasnt saying that rank, clan, duty etc. are worthless and only the pursuit of strength is important
his main point is that all these puruits are corupt because they make you lose sight of whats actually important
he never really defines what he deems as important, but it seems to me that all the other clan members are afraid of him because he does not succumb to the same corrupt values as everyone else
all of there beliefs/values are therefor threatened by itachi's existance
i have a feeling that the slaughtering of the clan isnt going to be initiated by itachi but will at least start as self defense