I don't think anyone is naturally good or evil. Besides which, there are a lot of things that can be swung either way. If you let a small underling who's personally killed a few people go free in order to catch a leader whose commands might bring death to hundreds or thousands, can that be totally evil or totally good? On the one hand, you let a person who you know for sure has killed walk free, but on the other you might prevent the deaths of so many more by doing so.
There might be an inclination to one or the other by nature, but I think it all boils down to a matter of all the experiences the person goes through, and the personality that forms because of those experiences. The human mind's way too complicated to ever know exactly how someone'll react to something, since it also depends on what experiences they had before. All those experiences/thoughts/encounters build up to make everyone who they are.
That why there are some people totally willing to give their own lives for a cause, and others think only of themselves. Some say this might also be why we're having so many problems with the Middle East and other areas. Apparently, the source might have been totally biased of course, the children there are raised to believe certain things, like the US is pure evil. Because they have no experiences to say otherwise, they grow up with it and eventually accept it as truth until it becomes such a part of themselves that they can't accept anything else. They're also raised to believe fully in the extreme forms of Islam, disregarding the peaceful nature of it entirely and using jihad (which apparently doesn't actually mean a holy war but really a struggle, and more of a struggle against one's own inner demons-correct me if my sources are again wrong) and the idea of heavenly salvation as a way of encouraging self-sacrifice. In other places, a person might find that his mindset allows him to truely enjoy helping others out, and becomes a truely generous giver. Others might find that doing good gets them respect, as others pointed out before, and do good just for that. Yet others might find that they really don't care about others, and try to serve or save themselves. Whatever the case, it's a case of what kind of experiences each person went through, and how they reacted to them and what they learned from them. These all determine how they'll react to things in the future. Well, that's my ideas on it.