Board Thread:Theories and Speculation/@comment-30172350-20170617091148/@comment-25122992-20170617101730

Because, as it's even stated in the trivia section of his page on the wikia, his actions contributed to the motivations of several major villains who became even more threats to Konoha when Danzo messed up their lifes for "the best for the village". By this, I mean mainly Nagato (Danzo's troups helped Hanzo in betraying Yahiko and this deepened Nagato's grudge on Konoha's shinobi), Kabuto (whom Danzo robbed off a real identity and then ordered to dispose of) and Sasuke (whose live was also messed up due of Danzo's orders to Itachi to wipe out their clan). Also, Danzo was chilling around and experimenting with the likes of Orochimaru.