That's a good point! I was literally thinking that. From a purely pragmatic point of view, Thorn is worth much less as a fighter if he has a phobia. What if he needs to go into a building and it's too tight for him? What if he freaks out and kills people or destroys things? I know Galbatorix is supposed to be mad, but, at least from his appearance in Inheritance, he had enough sense to keep the kingdom running, and to make a plan to subjugate magic users. Murtagh already has enough trauma; why throw in more?