Quote by Buz
If the 17 year old child possesses guns, the parents need to inform police. If they know and do not, they should be held responsible.
In theory this works, sure, but not in reality. In cases where parents are aware that their children are a threat to society, but they do nothing about it, then yeah, this is feasible. That's why when criminal charges against parents are pursued in this regard, it's successful. But blanketing it in the way you're presenting removes nuance, and once that happens, it runs the risk of it all being done away with, even when it's appropriate. And feeling as if your child is a threat, either to you as the parent or society as a whole, doesn't grant parents any protections from their child, only responsibility when things go awry.
There exists countless cases of parents (mostly mothers) being severely physically assaulted by their teenaged children, and having them arrested and pressing charges and everything, only to be called from the police station and told "Your child is being released. Don't really care if they're a threat to you, but if you don't come get them, you'll be arrested for neglect and/or child abandonment." And in such cases when parents are battered by their own children, the parents face legal repercussions if they defend themselves. It's a no-win situation.
The way I see it, when it's a clear case of overlooking on the parents' part when their children commit violent crimes, including mass shootings, there already exists a precedent for holding parents accountable. But there is no precedent for protecting parents from their violent children. And btw, it's a very outdated way of thinking that parents are the creator of these "monsters." Don't get me wrong, they often are when it comes to abuse/neglect, enabling, and otherwise lack of accountability, but even when these things aren't present and parents do what they're supposed to do, children still end up being whoever they want to be, and making the choices they make.