Why are many cops' kids messed up, like doing drugs, smoking, having promiscuous , etc?

Often times, cops have messed up kids who're screwed up in their personal, professional and community lives, why is that? One cop's son I know would go around trying to feel girls' while in school. Sick. Why is this so? Aren't cops supposed to be great role models with good family values and everything, especially with their own children?