Parents' job is to set an example and raise their kids the right way. But if a kid goes on does bad things, even though the parents taught them otherwise, the blame is on the kid who decides to do it. Like if the kid wants to go do drugs, it's the kid's fault for doing it. However if the parents did those kinda things, then it's their fault for influencing them.
Although parents do have influence over their children, they cannot control every action their child makes. We all make our own decisions. We are all responsible for ourselves. We should all suffer the consequences of our own actions. It is unfair to blame the parents or to hold parents responsible over something of which they have no control.
Parents train their children to whats right and whats wrong. They also train their children of the evils of the environment. As the saying goes "you can take a horse to the river but can not make it drink" so in the same manner your parents train you and thereafter the decision is yours.