No one's saying we shouldn't let the judicial system run its course. In fact, most of us can't wait for this guy to receive his justice. What is lamentable is the fact that so many weren't willing to look at the seemingly blatant signs and make a call, simply for fear of offending a group.
If you think that is why some of us reject the rush to judgement then you are dead wrong. The reason many of us here urge caution when trying to decipher this guy's motives or connections is that we really don't have a lot of clues right now. The people who know the best are the police and law enforcement who are investigating this, not members of a random internet forum.
The problem with relying on the earliest info, whether it be eyewitness reports or leaks from law enforcement, is that those reports are often inaccurate or just plain wrong. I find it a bit ironic that we are good at following correct procedure around here about mishaps and casualties but when it comes to an incident like this we seem to forget why it is a bad idea to rely on conjecture/rumors/leaks. Law enforcement investigations often have the same rules and customs, especially one like this.
A perfect example of relying on the early rumor/innuendo/leak is that the CIA is denying earlier reports that it has info relevant to the case and is refusing to share with others. And from what little I have seen it is not even clear if they had anything on him in the first place. The FBI will get all the info they need, Congress will too eventually, all they have to do is ask their CIA colleagues sitting next to them.
Calling the guy a terrorist doesn't change the fact that he killed 12 people. It does speak to his motivation, which will take the prosecution of justice down a far different track than "just some crazy who snapped."
Whatever label you want to stick on him, that is the important thing.