Call it soft, but in this world- this story was solved by messiah optimism. The manga tells us that Danzo, Pain, Itachi & Sasuke's ways were not right. They're rightfully villainized.
Characters with unreal optimism and naive dreams like Hashirama and Naruto win, because it's that gorgeous Shonen idea of 'what if people actually tried for Utopia for once'.
Just throwing in my two cents about the bold here:
Danzo and Itachi's way was terrible! Genocide is never the right answer and is an inexcusable atrocity. Even if they said, "Kill Fugaku" or "Kill the police force", that would have been one thing (not necessarily good, but better than the whole clan). However, it was inexcusable to kill every member of the race including civillian Uchihas and children who had no knowledge or involvement in the Uchiha coup.
Nagato's and Sasuke's ways: I understand the logic behind them, but I still don't fully agree with them. Nagato basically wanted to create the ultimate weapon of mass destruction, use it to induce the fear of war throughout the world, and end war (in temporary cycles) in this way. That idea is noble in its own right, but it has a fatal flaw:
Humans are stupid and selfish (not everyone on an individual level necessarily, but more so in a general sense). What I mean by this is: There are people in the world (both the real world and the fictional world), that simply do not fear death, and do not care about the harm that befalls others. They just want what they want no matter the cost. From what I hear, there is even a certain real-world leader of a certain country (I won't name any names for the sake of sensitivity) that said that he doesn't care if the world goes to nuclear war and he doesn't care if nuclear force is used against his own country. With people like that in power, even with Nagato's plan, eventually the world would still go to war, and this would most likely simply result in the destruction of the world at the hands of this weapon, rather than world peace.
Sasuke's way was essentially to become the world's common enemy (and basically its shadow ruler), and have peace be achieved by having everyone unite to oppose a common enemy (himself). Once again, I see the logic, but I feel like this plan is incomplete and involves too much sacrifice of the innocent.
For example, from the start he already wanted to kill the kages (at the time), the bijuus, and Naruto (the last one was more so for personal reasons). Already, you can argue that this is 13 innocents killed right there alone. Tsunade, Mei, and Gaara were not kages or in charge of their countries at the times that the previous wars and conflicts waged on, and Gaara wasn't even born for a number of past travesties. This can be said for Naruto as well. As for the bijuus, it is not their fault that people fought over them, and they certainly don't deserve death for that.
For anyone who says that the bijuus should be killed because of people fighting over them, you are basically the same as Hitler and many other racists and facists. Here is why: In real world history, many countries have fought over races such as Jews, Africans, and Native Americans for purposes such as enslavement, imperialism, displacing people to take their land, etc...
The Jews, Africans and Native Americans have been fought over. By your logic, should they be killed off? Well then how is that different from the bijuus? Does a race being fought over put that race at fault for everything, thereby making them deserving of genocide?
Digressing back to my original point, these 13 wouldn't be the only ones killed. Over time, people would get over the loss of original people who were killed. This acceptance, combined with the fact that no known living shinobi thus far (barring Naruto) could actually take Sasuke down, would lead people to ultimately continue on with their lives (which would inevitably mean that they'd eventually stop focusing on Sasuke and continue with warring amongst themselves). In order to reinstate this hatred towards himself, Sasuke would have to periodically kill more innocent people just to keep people focused on him.
That is what I mean by too much sacrifice of the innocent.
As for the incomplete part: Even if people did focus on him, that wouldn't actually resolve the other issues that people fight over in the first place. For example, people fight over land, resources, religion, political marriages, poverty/economics etc... Sasuke would just be one issue, but how would his presence as an enemy solve all of those other issues?
To be honest, I like Madara/Obito's way the best (if it wasn't for the whole white zetsu transformation). If everyone lived in their own personal dream world for eternity, then there would be no more inequality amongst humans, no more poverty, no more strife, no more conflict, no more pain or loss, etc...
Even if a person dreamed of there being strife and conflict, it wouldn't actually affect anyone else since everyone else would be living in their own dreams.
That is just my two cents.
