Do you think any child in any society that has ever existed.....would not consider bad......a person who went yelling loudly and killing everyone he could find?
Probably, if it had a concept of bad.
Do you think that is evil?
That is a sick person, or a soldier of some type, although soldiers always seek to kill within parameters. I don't like being in the vicinity of loud yelling, or certain kinds of loud music. But, that doesn't make it evil. If there was a person like that coming down the street toward me, i would likely attempt to put him out of his misery. But that doesn't mean that person was evil, just as a monkey that beats on other monkeys isn't evil.
A person could end up being like that for many reasons: bad brain chemistry, misunderstandings, bad decisions, bad luck, etc. Many of us fantasize at times of doing violence to others, but we don't because of fear of punishment, reflecting on how the other person or persons near to him might suffer as a result, laziness, lack of the ability or oportunity to carry it out, etc. The point is, in our hearts, some of us are like that, at times, but we don't manifest it. Is the action evil, but not the thought? My answer, neither is.
In cave man days, might was right, and so, a strong person doing the above was not considered evil, whereas, a weaker person doing the same would be dealt w quickly, because he might be considered as having done evil.
An example may be the cult compound at waco, texas being attacked by federal agents. Children inside may have percieved those men exactly the way you described. Yet, those men were not evil. They were doing a job that they were trained for, and were ordered by people of high authority to do.
SS