Why didn't Sarutobi kill Danzo? As I'm watching these filler episodes, I am wondering, why was Danzo still alive, after doing all the things he did to The Third? He hid a Wood style user, he tried to assassinate Sarutobi (not even once), he tried to lure the Anbu forces to join the Federation, he tried to manipulate the Hokage election after the death of Minato, and so on (just from these couple of episodes, without mentioning the whole "rivalry" between them).

The Third was aware of the situations, since he warned Danzo a lot of times. So even if he was a member of the Hokage's council, why did Sarutobi endure the disrespect and danger that came from Danzo? I would've been pleased even with a ban from the Village, but given what he had done, Sarutobi could've eliminated Danzo without any efforts.
Danzo was, in his own way, protecting the Hidden Leaf.

Danzo would normally do the "dirty work" and handle with that "black ops" of the Hidden Leaf, thus keeping the village officials clean.

They had their disagreements, and yes Danzo did act in order to dispose of the Third and have control over the Hidden Leaf, but Hiruzen always believed that all he's doing was for the best of the village, so he let it slide.