Maybe it's the difference between "people act good most of the time" and people truly being good. I don't think the vast majority of people are up to something criminal right this moment, but I might be less confident that 99% of people are motivated by good intentions. "Good intentions" and "not a criminal" are very different standards, but that's the point.
The fear thing made me think something else entirely: does it count as being good if a person acts good out of fear? (Of being caught/punished.) Everyone's answer to that question may also colour their views on peoples' goodness.
This just reminded me of an interesting idea one of my highschool teachers proposed: mother that doesn't love their child, but still performs all of her motherly duties because she feels a responsibility towards the child?
Is she worse than a mother that loves her child? Is she better because she can 'do the right thing' even though her feelings might opposed?
The fear thing made me think something else entirely: does it count as being good if a person acts good out of fear? (Of being caught/punished.) Everyone's answer to that question may also colour their views on peoples' goodness.