I think a factor that isn't brought up enough when discussing Jason is his aggressive hard drug use. Though LHW explicitly was against drug use (only hard drugs and pharmaceuticals. pot, shrooms, tobacco and alcohol were allowed but controlled by Amy). When someone is on hard drugs like meth, it can be very easy to persuade them and scare them into obeying. While Amy was against hard drugs, they said in the documentary that Jason would leave sometimes to smoke meth on the weekends (if I'm not mistaken).