one of our greatest philosophers (according to Nassim Nicholas Taleb of The black swan fame) Betrand Russel said this in his work "Why I am not a christian":
"The essence of the conception of righteousness, therefore, is to afford an outlet for sadism by cloaking cruelty as justice."
He leads this by claiming that righteousness implies unrighteousness, which I also agree with but with a slight modification. In grouping people you automatically create non-group members. This group mentality rather than individualistic thought gives us group justice which transcends the morals of man into a nether world of democratic truth. As soon as you fight for a cause, you begin to forget that the defenders are human too. Group members tend apply their group's actions to themselves personally, yet only admit to fighting the good fight against the oppositions inhumane causes when it's them committing similar atrocities.