human nature sampling error

If you think that all people are terrible scoundrels with the worst intentions, or that all people have good intentions underneath, or that all people are born innocent, or that all people are born with nothing but selfishness...then you need to meet more people. "Natural" behavior has a huge range which thwarts a right statistical sample. The depths are lower than expected and the heights are higher than expected. Since it's impossible for us to meet everyone, too often we fall into the trap of assuming that the much smaller group whom we've met is a good representation of the whole. This is a vital reason why a protected (but not necessarily isolated) upbringing helps to cultivate the willingness to believe the "best" about everyone until proven otherwise; rough defensive survival leads to the habit of perceiving threats all around.

The doctrine of Christianity is that human nature is fallen. We cannot create a paradise for ourselves, not even when we start with an extremely selective subgroup (Puritans?). But we retain our former glory to varying degrees. Either the inherent good or the inherent bad is exaggerated over time. In any case, the good isn't good enough. Regardless of someone's human nature in comparison with the rest of the populace, supernatural change is the prescription. Our limited samples of humanity tend to be incomplete evidence about the truth of human nature in one way or another, but God is not fooled.