I believe the goodness in man is an evolutionary trait of survival (as is evil, but more on that in the next question). Human societies seem to thrive when members collaborate. This can be seen in the explosion of agriculture around 8k years ago, which gave birth to the first real societies. Big institutions like governments, economies, armies, schools and companies would not exist without humans helping each other and collaborating for a greater good. That good is almost always self serving (ie survival). I don't think its a coincidence that some of the biggest outpouring of goodness in society usually follows big catastrophes. We help one another survive and thrive, so we must be good to each other.