Here's your main reason:
If ONE person is injured/killed within a 10 mile radius of a theater and the person doing the killing proclaims any notion of it being done because of the release of the movie, the relatives of the one shot will sue Sony for millions of dollars due to the release of the film that Sony KNEW could unleash terrorism. Imagine if it happened at 5 locations? What about one nutjob in one theater ala the Batman movie a few years ago? Sony would be put at fault for blatantly disregarding public safety by knowingly releasing a film. It's the same reason newspapers won't print an image of Mohammed or that South Park had to pull an episode that was going to show Mohammed.
Hyper-sensitivity to everything for fear of litigation.