Huh. Call the parents responsible for what their "child" does? That would probably have to end at 18 (with current laws), thus this Ramos guy would not be included. My guess is that grandma, whom he killed, was the only parent raising him.
I see you probably have also read about the Columbine situation. It's an interesting idea that you are suggesting that the parents should have been more prying, more suspicious, more AWARE of the really Satanic communications their kids were making. Especially Eric. Dylan was some sort of compulsive dependent follower ---- majorly suicidal, too.
I don't know: this is the sort of accusation people always throw around, like at the wife of the BTK serial killer ---- that she MUST have known! And the family of that one in California who was outed lately, who raped and killed really dozens. And it's a favorite fictional theme --- when does a wife or daughter start suspecting such a thing? I think this may be a bridge too far for imagination of most normal people. How could one think such a thing? I can remember betrayals in my life that seemed serious at the time, but they were NOTHING relative to a husband/father being a serial killer or a son being a mass murderer, and yet it took me years and years to "grok" what must have happened.
Still, I think you have a good point. Make the relatives responsible, and it WOULD encourage a salutary suspicion. Especially with these angry suicidal shooters. There is too much denial going on, you are perhaps right about that.