Cognitive Dissonance.  "When OUR team does it, for a just cause, it's MORAL!"
It was talked about in the book 1984, when in the high ranking party members office, the main character was questioned, how far would he go to free everyone?  He said he would throw acid in a childs face, among other horrors, if it meant freedom.  And this is where we see that when one sinks to the level of their enemies, everything they were fighting for anyway becomes lost…and so you have the birth of Cognitive Dissonance, it allows them to do anything and everything while remaining morally superior.
It is the most dangerous thing on the planet.