If it makes you feel any better, if he tried this with another dog, one who wasn't fearful or overly submissive but healthy in mind and body, he'd likely get his aggressive behavior met with equal hostility - a warning growl, snap or nip or outright fight until he learned to stop that unstable type of behavior. Other dogs don't like instability and will discipline a dog displaying it. So the mere act of your son merely picking him up in his arms is nowhere near the type of justice another dog would naturally and instinctively mete out to him.
__________________  Jeanie and Tibbe One must do the best one can. You may get some marks for a very imperfect answer: you will certainly get none for leaving the question alone. C. S. Lewis |