Fugaku and his inner circle weren't some radicals, he was the respected leader of the clan and you seem to be very naive if you think simply putting a leader in prison means they no longer wield power and everyone is just going to give up.
I'm not naive. You're paranoid. Any regime can be toppled by quick, decisive action and rapid improvements to pacify the discontents. If they have no reason to be angry, then they have no reason to keep fighting. It's that simple. It's not about hoping they'll make a moral decision, it's about giving two clear outcomes: fight us and die under your old leader, or live and reap the benefits under the new leader.
If the Uchiha clan turned their back Uchiha Madara, they'll shouldn't have had any problem turning their back on Uchiha fucking Fugaku.
You have to completely discredit leaders to take away their power and Konoha were in no position to do that to Fugaku. There is no getting around that taking Fugaku prisoner destroys the very last amount of trust between Konoha and The Uchiha.
Fugaku would be completely discredited if his replacements improved conditions for the clan as a whole without shedding a single drop of blood. It would be undeniable proof that radical action was foolhardy and ill advised, and it would inspire confidence in the system.
What resistance remained after the hardliners would be quelled at least for a time, during which, rather than let it fester, it could be dealt with.
Why in gods name would they listen to a damn thing Hiruzen and Shisui says or tries to do when their real leaders are behind bars? The normal Uchiha who don't know anything are all going to end up turning against Konoha for what they see as a power play and unjust imprisonment. If Hiruzen tries to say they were plotting a coup, well then who are the Uchiha going to believe, the government that resents and spies on them or the leaders who they all respect and revere? Shisui won't get a chance to "make things better" he'll be a traitor trying to usurp the throne.
Because their "real leaders" were going to get them wiped out whereas the new one would do actual good and better their lives without risking it on something as ridiculous as a coup.
Shisui would have to earn their trust by acting in their best interest, something he would have an easier time than the previous regime seeing as the Hokage would have then just gone through the effort of preventing a coup in the first place and wouldn't want to waste that progress by stonewalling the Uchiha again.
You plan relies on so many assumptions, ifs, and naive hopes that the Uchiha are just going to "come around" and everything will go perfectly, Danzo took it out by the roots and wasn't going to leave anything to chance.
No, it doesn't. You are ill misguided if you think the entire Uchiha clan, including those that had ordinary lives outside out of MP, would rather rebel and die a pointless death than reap the benefits under new leadership. That's stupid on the face of it.
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