Karin & Uchiha family parallel of Itachi and Sasuke mentality
I don't know why this did not occur to me sooner!
The same principal and logic that was in Sasuke's head when he shot Karin is almost identical to Itachi's logic when he murdered his family. To achieve a goal, human life is nothing.
Itachi wanted to spare Sasuke the grief of going over the Uchiha plans AND save him from whatever Danzo had in store. You could say Itachi was blackmailed. You could say he was just operating under orders. The fact still remains that Itachi had a target goal and he worked on it, life of people is thrown aside and does not matter (nor does his own).
Sasuke was intending to kill Danzo and wants vengence for himself and justice for his family, no matter the cost. (Just like Itachi, "no matter the cost"). Human life is tossed aside. It is just about achieving that goal.