Are people naturally good and fair? Or are people vile and cruel in their natural state?
Naturally good. The whole video is great, but @5:40 is where it addresses your post.
Neither. We learn what creates results in our lives and gets us what we want. I do think there's a difference though and that 'good' actions are more satisfying than 'bad' actions. But someone who took the bad route in life probably never experienced many situations where being good got them what they wanted.
There is a quote that I am in love with it's from Avatar: The Last Airbender, and it goes something along the lines of "Anyone is capable of great good and great evil."
It is what we choose.
Found the quote.