There is also the
possibility that Tobirama's version of Edo
tensai is different from orochimaru's and
might actually bring the person back to normal.
@ericdana73 the theory of killing your
best friend to gain the Mangekyo Saringan has been
disapproved. So far no uchiha has gained it in
this way. Not even Sasuke, who got it when he got
to know who his brother really was and then coming
to the realization of lossing him. Tobirama says
its when they loose a great bond first seen when
sasuke protects naruto who he thinks is about to
die by haku then again when sasuke severs his bond
with naruto at the valley of the end.
That would essentially defeat the purpose of
killing Izuna Uchiha. If Tobirama had been able to
use the technique and just bought back Izuna it
would just put them back to square one. Yeah
there's a possiblity that the clans would
have been at peace, but then who knows how long
that peace would have gone on for. If Edo Tensei
can bring a person back in mint condition then
that just makes the Uchiha the same threat that
they were from the start.