I understand your point as well. Obviously we differ in our moral codes. The regulation of the consumption of fictional media, sparked by the desire to suppress "immoral" thoughts, falls into the area of criminalizing thoughtcrime (in Orwell's definition/coining of the word) for me. The justification seems to be certain thoughts or feelings are, in and of themselves, evil acts. I only assign moral value to actions which occur externally from the mind. An absurdist, but true, example would be courts declaring sex offenders can't possess completely legal (for the rest of us) materials such a video of young girls cheerleading or a swimsuit catalog with sub-18-year olds inside, because they will have evil thoughts about the girls within.
Yes, I know. Really the crime that the courts are trying to stop is "vile thoughts while masturbating." I don't see how this affects anyone else.
I am familiar with the idea that evil thoughts lead to evil actions. Buddhism makes it fairly clear in two parts of the eight-fold path--"right thought/right action." But I don't see where legislation to produce right thought which leads to right action has any logical end. Also, people have had no problem thinking bad thoughts which lead to evil actions without media to spur them on since the beginning of history.
But works made by monsters to showcase their cruelty featuring real-life victims are ipso facto evil actions. Even if the direct victims are dead. (As others have stated, their living loved ones can be victimized as well.) I'm not saying any material along these lines should automatically banned for ownership by the public, but they are some of the few bits of 'speech' for which I see a solid rational justification for banning.
A related point: the point of terrorism is to create a reaction by government in response to the horror of the public to the terrorist act. It looks like this guy would be justified in feeling he accomplished his goal at the moment. What fictionalized account of the video could do more damage to gun rights, and civil rights in general, than what is actually in the video?