The belief that people are inherently good is a tempting one. One of the argument for this belief is that everyone wants to present oneself as good, and perceive self as good. This positive value attached to goodness is often mistaken as people being inherently good. But the reality is complex.
John Locke in 19th Century proposed that people are born with a "clean slate," or tabula rasa. This means that the beliefs and principles are acquired from the society. The positive value attached to goodness is also an acquired one.
Further, goodness is also a social concept. In absolute terms there can be nothing good or bad. It is only when we apply an action or a principle in a social context, it is labeled as good or bad based on critera set by the society at a given point of time. It gets more complex if we take into account the individual subjectivity.
Therefore, people seem to be inherently good because there is a social reward associated with goodness.