What exactly did Remington do that was wrong? Manufacture and sell a legal product in accordance with Federal law? It was the kid’s parents that brought the firearm into the home and let their obviously deranged child have access to it.
The kid murdered his mother in order to gain access to the firearm. The kid's father was no longer married to or involved with the kid.
It is certainly possible to debate the wisdom of every aspect of the care provided to the shooter, including having a firearm present that he could murder someone to obtain, but there is either blame all along the path of the shooter's life, or he is responsible for his actions.
Blaming the parents, including a father who wasn't even there is unjustified.
This has been ongoing for so long now, I forget the details... though I think it was something to do with the way Bushmaster (Remington) chose to advertise the rifle.