In protecting the whole village as the true Hokage, there had to be some collateral damage..
The killing of the Uchiha was just collateral damage as a result of keeping the village safe..
If the Uchiha clan hadn't been wiped off, more lives would have been lost..
Itachi knew this and took a stand for the greater good..
Collateral damage that was avoidable. Hiruzen came down hard on Danzo, for end running him. Danzo and Obito both shared the Uchiha's sharingan post massacre to further their own ends.
The Uchiha are apart of the village. You can't destroy an entire community of people, turn around and say you saved it. Itachi and Obito murdered the Uchiha, just to allow Danzo, Hiruzen, Hamura and Koharu to build a lie around the circumstances of their deaths.
I doubt that. The Uchiha lost the element of surprise. The Hokage, leader of ANBU and village elders all knew about the Uchiha's plan. What was stopping Hiruzen from martialing the Jonin, ANBU, and members from the various clans of the village (Hyuga, Yamanaka, Akimichi, Inazuka, Nara, Shimura, Sarutobi, Aburame etc) and marching on the Uchiha before they could enact their plan.
Keep in mind these little tidbits.
The appearance of the sharingan is rare.
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The Mangekyou Sharingan is rare for people who have the sharingan.
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And the strongest Mangekyuo technique, susanoo; being even rarer.
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So the idea that the Uchiha clan were going end the village with their "awesome skills" is ludicrous. Only a handful of Uchiha were ever truly exceptional. Plus the Uchiha didn't have the numbers to win. They would've fought very bravely and died very quickly. Like their distant cousins of the Kaguya clan, who similarly launched a coup against the Mist Village.
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Danzo TNJ'ed Itachi in to killing the Uchiha, because he wanted to exploit their power. Something Orochimaru was happy to do with his experiments on Hashi cells, Izanagi and the creation of the Shins.