Why this guilt discrepancy in human beings? I believe no person is born a criminal.

Then why do some people have compunctious guilt after a wrongdoing even when they were raised in an unhealthy family and some people have no guilt at all even when they were raised in a healthy family?

Why this guilt discrepancy in human beings?
Lack of guilt is related to psychopathy, although there could be other reasons for it, e.g. ideological self-justifications, like breaking a law you don't agree with. Psychopathy is partially inheritable, which means the genetically-unexplained variance is usually attributed to enivronmetal differences.

The propensity for guiltlessness is part of a narrower trait (of psychopathy) called "callous-unemotional traits", and these can be identified around the age of 7, according to one (fairly cited) study of Viding 
 et al. (2005). Although the abstract of this paper is a bit... abstract, its intro is a bit more insightful what it is talking about:


  ‘Mark does not feel guilty if he has done something
  wrong, he does not show feelings or emotions, and he
  is rarely helpful if someone is hurt.’ This description
  of one of the 7-year-old children (name changed) in
  our twin study captures the core emotional impairment
  of individuals with psychopathy. Psychopathy
  in both childhood (psychopathic tendencies) and
  adulthood involves both affective-interpersonal
  impairment (callous-unemotional traits; e.g., lack of
  empathy, lack of guilt, shallow emotions) and overt
  antisocial behaviour.