Uchiha weakness discussion.
Due to all of the recent happenings in the manga and previous excursions with Danzo, these are my opinions/ideas on why Uchiha go blind from the over use of Mangekyo.
1) Uchiha did not inherit the physical stamina of the sage of which they are descended. This plays a major part of my idea because use of the Mangekyo could drain physical energies associated with the eyes. To explain consider that there is a physical energy/stamina as well as a spiritual energy/chakra. Draining of this physical energy could be the reason for blindness. We all know that Uchiha have a good spiritual energy, so they have decent chakra levels, which is used to "cast" the techniques.
2) Users that have not been Uchiha have never suffered blindness, save from izanagi. This might mean that since there is no proof or mention that Kakashi or Danzo have senju DNA they still have above Uchiha level physical energy. They might have slight lineage from senju which gives them more, but we can only speculate that as we don't know for sure.
3) Obito has senju DNA increasing the physical energies he has.
4) EMS is the perfect form no longer draining physical energy. Plus repairs previous damage. This means that limits could be removed allowing better techniques that would have cost too much physical energy.
5) Kurama restores the physical energy as well as chakra making it so Kakashi can keep spamming. Karin only restored chakra on Sasuke so he didn't have all his physical energy back to keep spamming.
6) Itachi because of his disease had extremely low physical energy, this would explain his non-spamming like the other characters. This is the saddest realization to me, because Itachi has always been one of my favorite characters.
These ideas could explain why Sasuke unfortunately before EMS was the only major candidate for blindness.
Please discuss and give counter examples or other thoughts!