The sharigan versus the rinnegan
This is not your typical sharingan vs rinnegan thread, it is a thread going into what this these two doujutsu symbolize. I've written a few of these threads today, and I'm sure you're ready for me to finish so this will be my last one for today (and probably ever knowing me haha)
I believe that the sharingan and the rinnegan can be seen as the two different ways in which people perceive the world.
Sharingan users: Itachi, Sasuke, Madara, Shisui, Izuna, Obito, random Uchiha fodder, i'm sure i'm forgetting someone.. (kakashi doesn't count since he has a normal eye)
Rinnegan users: SO6P, Nagato, Madara, Obito (not sure if he should count for my purposes since he has one sharingan eye)
With the exception of Itachi and Shisui, the Sharingan users have been portrayed as focused on their own personal power and hatred. The classic example of this is Obito's story to Naruto and Kakashi of the Uchiha clan's curse of hate.
Another example of the perception of the world inherited by Sharingan users is that you have to kill someone close to you in order to attain MS. I think this is the best example of how the Sharingan symbolizes a distorted way of perceiving the world, and the motivation for personal power at any cost Sharingan users have.
On the other hand Rinnegan users, have been more focused on the whole world and creating a system that fosters peace. In fact in the manga when Kishi presents us with old Madara after having awakened the Rinnegan it is in the same instance that we hear that really all he wants to do create a better world. I think this change in Madara's doujutsu is a reflection not just of his pursuit of power, but also his change in the perception of the world and his purpose in life.
Nagato is also an interesting example of a Rinnegan users perception of the world. At first glance it looks like he is obsessed with hatred and the pain of that hatred as the general Sharingan user, but I think the key to this lies in Nagato's ambition. Ultimately, Nagato's concern isn't just with his own hatred, but creating a better world.
That is not to say I think that the sort of change in perception is a requirement for the Rinnegan
But I do think that this shows how the doujutsu's reflect the character's perception of the world and their purpose in life.