[grayhatter]

It's not clear cut, but the metrics chosen are important. If you care about drug use more than violence, it does seem to be clear cut. Same for the inverse.

You bear no responsibility. Everyone must take responsibility for their own actions.

I have a kid, I raise him to the best of my ability, and commit no egregious mistakes. He grows up and murders someone. Am I at fault? Obviously not, just because I'm a part of the equation, doesn't mean I also should be assigned blame. If I didn't have a kid, [person] would still be alive. That doesn't mean I'm responsible.

[pessimizer]

That parents' behavior has no effect on their children is not a universal belief. I think that a belief that one bears no blame for what one's children do is a way to inevitably raise terrible children. That's like not having any responsibility for whether the product you built works, or is toxic.

edit: blame isn't exclusive; everybody can have 100% of it. Although IMO blaming children for what they've done (however you define the age of majority) is almost entirely scapegoating. You might as well convict a dog or a pig as an adult if you would convict a 13 year old.

[drwiggly]

That isn't the same. After you raised your kid you don't control their environment. Does an environment contribute to individuals actions? Consider the thin blue line. Populations under duress and their cooperation with authorities.