There's gotta be some kind of Game of Thrones-level evil/perverted intrigue going on. My hunch: Hunter's rage for always being the unfavored son, combined with his anger at Pops stealing his daughter Finnegan from him (this is a family where there is no shame, Hunter probably started having incestuous relations with her when she was little) - drove him to get revenge at Pops by defiling Beau's daughter, and conveniently getting the laptop to the public by "forgetting" it at the repair shop. He figures that since he's going down he'll burn the whole family with him.

It's like the tragic universe of a Russian novel, no heroes or good people, only victims and villains.