Good or Evil? (Master Lecture)

I've been asked this question a couple of times and I had answered it on different views as well. After reading Sun Tzu's Art of War I am already convinced that human beings are naturally evil. I may sound a bit morbid, but come to think of it people from the past kill each other for survival. There are a lot of fearful and horrifying things human beings can do.

Example of this would be a soldier who has been in the war for 10 years deprived of the things he used to have. After the war the soldier tend to change his/her attitude and becomes grumpy, always mad (evil like attitude). Others say this is becuase of the psychological change or rather the traumatice experience war gave but this just brought out the real personality of the person's human being.

I guess the reason why there are people who tend to be good is that they have found the sense of having a sanctuary (a resting place). But once that sanctuary as they call it is taken away, they'll change into something bad. This does not mean that they are naturally good. It just so happens that there is something holding them to be good, but if they lose all the reasons to maintain the goodness in them then the true natural attitude of the human beings will be brought out. Also, if human beings are naturally good why do we ever think of killing? or violence? and other "evil doings"? If good is the natural attitude of humans then we should have thought of other actions to settle things. But no, ever since our history can detect war and violence had been there, the option of those who lost options and the hope of those who are about to lose.