He didn't kill the frog to save Naruto, for sure, especially in regards to what he said afterwards about Naruto "No longer being in the way"
Originally Posted by sasuke123uchiha
Danzou wouldn't be able to destroy Konoha single-handedly, though; otherwise, he would've done it already, or when the village was weak after the 3rd died, jiraiya was out of the way, and kakashi was sick.
Originally Posted by 6thKage
Idk, Danzou's overall mood while he was killing the frog, and the lighting and stuff used when Danzou said the thing about Naruto didn't really seem like Madara, so mind control seems to be out of the question.
Originally Posted by Kakashi.
Danzou and the other elders were behind the destruction of the Uchiha. The possibility that one or more of them are working for Madara is very real. Madara could have told them to order Itachi to kill all the Uchiha, and Madara knew Itachi would never kill Sasuke, thereby leading to his first secret element of his plan of "the corruption of sasuke".
Then, Sasuke grows up, hating his brother and feeling alone, depressed, angry, and full of hatred, planting a seed of corruption within him. Sasuke continues to attempt to gain more and more power to defeat Itachi; his lust for power to gain his ultimate revenge further draws him to evil.
Then, Madara orders Pein to order Itachi to retrieve Naruto, possibly even trying to get Itachi killed, due to the fact that Jiraiya is with him. Sasuke hurries to where Naruto and Jiraiya are, and confronts Itachi. Itachi easily defeats Sasuke, further nourishing the hatred within him. Even Itachi, to some extent, was trying to turn Sasuke evil.
The thing that tipped him over the edge, however, was when Sasuke saw that Naruto's rasengan was stronger than his chidori, planting jealousy within him along with everything else.
When the Sound Five came along to take Sasuke to Orochimaru, he obviously accepted.
The things I've bolded are all aspects of Sasuke's life and personality that have been planted into him by Madara, through a complicated plan. All of them led Sasuke to the side of evil.
All of this started with Danzou, though, when he and the other elders ordered the destruction of the Uchiha.
But, what we've seen in countless films and animes featuring this theme of corruption, we know that the corrupted character always has the chance to turn good again. This was seen in Star Wars, where Anakin was turned to the dark side, but with his dying breaths, saved his son from the Emporer.
This theme is even seen in my own fanfiction, but due to the fact that it isn't finished yet, I cannot divulge more.