Hashirama is messed up. He's the cause of everything. His elitism has no bounds. And like in real life, it causes nothing but conflict.
Imagine a few things that could've happened opposite:
1. Izuna survives
2. Tobirama is killed
3. Sasuke is killed before the coup
Judging by the personality of Hashirama, he'd likely have gone emo. That's what elitists do when their sole purpose is denied. He already almost did himself in, when offered a choice between himself and his brother, so unlike Madara, he'd have collapsed.
Izuna would have supported his brother in his quest. He'd be that "Uchiha sibling battery" to make sure Madara remains sane. Madara in turn could've supported Hashirama in his mental crisis.
Tobirama, that paranoid ***hole, wouldn't have forced Madara to rethink his dream. Seriously, what did Tobirama do in the series? He killed Izuna in what practically has been sparring(I doubt Hashy and Maddy would've killed each other back then, and it didn't seem like Izuna made any progress). He kept hating Uchiha. He promoted Hashy as First Hokage and aimed to be Second. He secluded Uchiha. Christ, he probably has inherited the Will of K*****!
As for Itachi - he would've ended up as Madara. Plain and simple.
These two mentalities are so intertwined, but they can't figure out their priorities. All it takes for Uchiha to be happy - is to have somebody close to them. All it takes for Senju to be happy - is to be superior. Well, throughout the story - Senju are patted on the back. Class V mutant Hashy, spoiled brat Toby, Dumb-eldore Hiruzen and Harakiri Minato, who gave birth to probably most powerful idiot to ever live.
What happened to Uchina? Izuna dead, killed by the spoiled brat. Rin dead, killed by none other than the superior Kakashi(even if she jumped on Raikiri, she didn't genjutsu it out). Itachi twisted for the sake of "superior" Senju. Sasuke twisted not to take part in all this mess(doh, Itachi really hasn't thought this one through).
If anything, it's the Uchiha who have suffered at the hands of Senju, who used their superiority for nothing but elitism and entitlement. Hashy to become Hokage. Kakashi to fulfil his "for the sake of the village" assassination. Hiruzen/Danzo to wash their hands. As for Sasuke... well, technically he hasn't been used by Senju, but he was used by his brother, who tunnelvisioned into Senju mentality so much that he was ready to give himself up for his brother, instead of thinking first(kind of reminds the way Hashy would rather kill himself than reconsider about his brother). At least before ascension, he figured that probably assassinating the clan and leading his beloved brother through something what would make Naruto look like the happiest child alive - was not the smartest idea.
Kudos to Kishimoto, he sure can protract the plot. Not that I don't like it.
Edit: I have to concur with people - Sasuke's revelation has been way to simple. Hashimara was supposed to explain Sasuke - what the F is this precious village. As it was - it's nothing more than an entitled dream of Hashirama, built on the bones of Uchiha. And Hashirama's story may have resembled Itachi's determination, but... so what? "Hurray, I don't have to be evil and **y(thanks to Karin) anymore"? So much for the darkness that shrouded even Danzo/Gaara. But... technically he can't be blamed(not to mention that it's all fictional). Itachi or Dumb-eldore are to be blamed. One has self"less"ly set his only sibling against himself, and the other was stupid enough not to ever divulge the story and prevent pretty much all the "Orochimaru is bad", "Obito manipulates Sasuke" nonsense. Sasuke was just made evil, then shown that he is not evil. Poor guy, really... Intended to stay away from all of this, he ended up the main puppet of the series...