As I stated before, the Uchiha could easily have gotten around the blindness by stockpiling eyes. Heck, they would not even need to hurt their own to do that. With the constant warfare during the pre-village area their would be plenty of corpses from which they could harvest eyes, and seeing how powerful the sharingan is it's actually a pretty good for the Uchiha to harvest the eyes of their dead since it not only allows them to spam their strongest techs, but also stops enemies from getting their hands on sharigan.(which could be implanted alla Kakashi by enemies, or studied for their secrets and possible counters to sharingan techs ect...) The bigger inconstancy is not the fact that the Uchiha spammed Izanami, but rather that they even had it in the first place. As I recall, Tobi said the jutsu could only be used by one whom possesses Senju and Uchiha DNA. I find it highly unlikely that so many Uchiha stole Senju DNA and as a result that whole chapter stank of retcon.