The statement should have read. Human nature is bad or Human nature is good. As written the question is open to either.
Human nature is neither good or bad, it's a matter of the level self interest or selflessness when acting upon others. Depending on what side you are on, war can be seen as good or bad; it's subjective.
Morality is the construct upon which this entire question is based. Let me remove that bit for you. Ah there we go, human nature isn't good or bad, it simply is. We cannot pretend to know our true nature, we still have no scientific evidence of our own existence, however, we can accept the fact that we are part of nature and thus our nature is quite lacking in the moral department.