The "Good Guys" are fighting the "Bad Guys" because the "Bad Guys" do "Bad Guy Stuff". It is taken as normal that the "Bad Guys" are "Bad". When they do "Bad

The "Good Guys" are fighting the "Bad Guys" because the "Bad Guys" do "Bad Guy Stuff". It is taken as normal that the "Bad Guys" are "Bad". When they do "Bad Guy Stuff", it is further justification for the "Good Guys" continuing to target them. "Normal" does not mean "OK", it just means that it is what is expected - "Bad Guys are Bad" is not news. It is morally outrageous when the "Good Guys" do "Bad Guy Stuff", because it calls into question the whole "We are good, they are bad" story that the "Good folk at home" are told. How can we be the "Good Guys" if we are killing innocents? It also reinforces the "We are good, they are bad" story that the "Bad Guys" are selling their folk at home. When the "Great Satan" kills your innocent friends and family when they are at work picking pine nuts, or at a wedding, it becomes easier to encourage you to take up arms against them.