Originally Posted by Vengeance
The Uchiha secrets are killing your closest loved one for MS, fusing your MS eyes with your brothers MS eyes to gain PMS, & the power to control Kyuubi this shit is cannon.....
No offense, that's not a "purpose" for the clan's Sharingan to serve.
What Itachi said was something along the lines of: "what *purpose* the doujutsu of the clan originally served"
I think that this may go back to how the Sharingan came into existence itself and what that four-eyed monster has to do with it.