Tobirama started the oppression of the Uchiha. Hiruzen left Danzo on a loose leash. If anything those three are to blame, especially Danzo. They blamed Itachi because they didn't know the real story.
I heard that Shanks would've KO'd all 100,000 with relative ease. I mean we saw what he did to Whitebeards ship and the lower lvl pirates on board just by having his guard up.