Whatever our origins and beliefs, we all agree that there exists idealistic concepts called good and evil. We all agree that they are distinct from each other, nothing can be both and that together they form the whole set of morality judgments. Things are either good or they are evil. Our categorizations may differ somewhat, as the concepts are deemed to be relative and can be localized, but our world has shrunk enough lately so that we all pretty much agree on nearly similar definitions.
Since these are ideas of the highest order, to be truly civilized we must come to understand them to have only universal definitions. Where they change from society to society, region to region, the cause is our own immaturity; our own lack of progress. Not the ideas.
Despite our infancy, we do know some things for certain. For instance, the cause can never justify the actions. You cannot do something evil, to justify something good. If your actions are evil, the cause becomes evil too, no matter how noble. Evil begets evil and always has, that's part of its definition.
We know that any significant power, held long enough by the same person turns toward evil. No matter how it starts, it always ends badly. They may start with the best of intentions, but it always goes down hill, and it goes down way sooner than you'd ever expect that it would. They always deny it, and they are always wrong.
Oppression of any type, for any reason is evil. Some control must be maintained, but anything beyond its minimal use quickly turns to evil. Making someone bend to your will is evil, and even more so if your reasons for doing it are selfish. Rules without real justification are evil. If you cannot prove, beyond all doubt that it is wrong or dangerous, then forbidding it is just oppression. Not saying why it is forbidden is also oppression.
Death and destruction are always bad, but they are undoubtedly evil when they get applied to innocents. And innocence is not something that you can take away because of the region of the world in which you live. It is universal, we all start with it, and it is only removed if we choose to do so actively. You were born innocent, it is your birthright. You stay that way, until you 'choose' to do something to change that.
Someone will always try to tell us what is good and what is bad. This is the most serious problem we face today. Most of us are too quick to give up our judgment to experts. That is wrong, if we have one and only one real responsibility to mankind it is to decide for ourself -- individually, all on our own -- what is good and what is evil. You cannot let others make that choice for you, no matter what organization, society, tradition or other factor they abuse to justify their claim. They have none.
As we seek to become the beings that we could be, and to build the societies that best expresses our potential, we face the challenges of our legacies. Not only evolution, but also our own histories constantly drag us back into their depths of our less noble beginnings. Even if you restrict the timetable to the last couple of millenniums, we still see our collective rise to become more complex. We are growing as a species. Don't let anyone justify a downward spiral back towards the abuses of the past just because they have twisted the interpretation of the present. You need to decide for yourself what is good and what is evil, it is the only way we can all survive. That responsibility is universal and it applies to all of mankind, no matter what we believe.