I don't think joshua is responsible.
It was his parents and the way they behaved.
Annoying as a child is, evil perhaps, you do not hit children.
As a parent I found it difficult to watch those parts...
The boy has serious mental issues that clearly ran in the family.
Sad but watchable film...
I agree with you. The parents (especially the mother) made it so obvious they preferred their daughter over their son. I believe his bizarre behavior (such as giving away all of his toys, cutting open the stuffed animal, collapsing at the piano recital, suddenly rethinking his religion, etc.) was a desperate attempt to get the attention he deserved from his parents. But when it didn't work and the attention still was focused completely on his sister, that was when he developed the plan to live with his uncle because he was the only one he truly loved. The parents were not the right people to take care of such an unusual child like Joshua.
Come, fly the teeth of the wind. Share my wings.