Despite Danzo's checkered and controversial past, many of his actions have been for a good (or at the very least, understandable) reason. As Danzo has numerous redeeming qualities, fans have come to sympathize with him and consider him as worthy of redemption as Naruto's other rogues.
Sasuke Uchiha was quickly becoming an international problem. In addition to sabotaging the Five Kage summit, he attacked whoever he felt like and swore to destroy the Leaf on numerous occasions. Although forced to fight, Danzo risked dozens of Izanagi sharingan in order to defeat him and was even willing to kill Obito afterward.
In the end, Danzo proved so determined to take Sasuke down that he gave his life in what he hoped would be a fatal attack. In his final moments, Danzo wished for Hiruzen's acknowledgment and prayed that he upheld the will of fire.