Good and evil are relative concepts, no matter how much the morally outraged or religiously sincere may want to believe otherwise.
They are relative to the norms of a particular group, a particular time, a particular place. They evolve, sometimes slowly, sometimes rapidly, as society adjusts to new circumstances, or as we seek expedient justifications for our actions. The more things we label as absolute good or absolute evil, the more they start to conflict with each other. Sadly, in the US at least, good and evil are often defined in courtrooms, and good and evil get confused with justice and injustice.
If we step outside of the narrow frames of reference of say Iraqis v. Americans, Palestinians v. Israelis, or Hutus v. Tutsis, and look at this little planet as an ecosystem, nobody can objectively deny the relative evil of homo sapiens v. any other species. Our capacity for deliberate or negligent annihilation of entire species in our quest for lebensraum or a better quality of life is possibly a defining characteristic of our humanity.
Evil is an attitude that can be passive or active. To do evil does not require a desire to do harm with an action, simply a disregard for the consequences that action may have for others.
If a person, a nation, a race, or a religion has enough power, will, and self righteousness, any evil they do can be spun as heroic.
Incidentally, for a great insight into some of these issues, I recommend Robert Kaplan's wonderfully written book "Warrior Politics - why leadership demands a pagan ethos". He draws on historical works from Confucius to Aristotle to Machiavelli and draws parallels with current leaders, nations, and conflict situations. The bottom line appears to be that the world has gotten way too small for one nation's isolated ideologies to be forcibly imposed on another's, and that compromise, tolerance, and co-existence are the only way forward.