Whether or not this is about behavior, due to some degree of mental illness, both parents and step-mother, especially the father, seem completely out of touch with their son's very real and obvious psychiatric and emotional problems to the degree of appearing themselves part of the problem, if not even the trigger of the escalation.
But I am not sure what the movie was telling us? Somewhere between script, direction and editing the whole thing got either diluted to indecisiveness of message, or confusion about the moral we were supposed to walk away with.
Even the actors seemed confused as to how they were supposed to deliver their parts.
It could be argued that real life is like that, but I've had 64 years of it and I would disagree.
The kid had real psychiatric issues and he was even explaining them to his parents, who were competitive go-getters by nature and they seemed to be in total denial of their son's reality.
I think the movie was a good idea badly executed.