Right so if someone breaks into your house and steals your rifle, then goes out and kills someone, you should be responsible for that as well?
If a parent leaves his/her weapons lying around the house and fully loaded, and a 6 year old child stumbles across it and accidentaly shoots himself or someone else, then yes, those parents should be held responsible. What we're talking about here though is parents who undoubtedly stored their weapons in an appropriate manner, whose teenage children decided to take those weapons without permission, load them, drive over to someone elses house, and then put a few bullets through the windows. There's a BIG difference between the two scenarios. One is a tragic accident caused by the negligence of the parents and the ignorance of a child. The other is several seperate crimes commited willingly by individuals who are old enough to know exactly what the repercussions of their actions would be. If you hold the parents responsible for something like that, where do you draw the line? Is a parent responsible if his 16 year old offspring decides to steal the family car and commit vehicular homicide? What about a teen who stabs someone with a knife from the kitchen? The parents provided access to the knife, so they're responsible, right?