The Aurora shooter was just one example, how about Sandy Hook? Or any of the others?
It's true that anyone with a basic knowledge of chemistry and an anarchist cookbook can bake up some terrible results. Trust me, I probably know it better than most people here. As I got arrested when I was in the ninth grade for fooling around with that kind of stuff (although exploding a tree was the extent of my adventures).
All I'm trying to say is that for the average person a gun is the most destructive thing available. A person who is emotionally unbalanced can reach for a gun and do the deed. Whereas if they have to manufacture an explosive you're looking at some time, time to stop and think. Plus pulling it off is tricky too, you have to manufacture or obtain a detonator, you need a timer, etc.
The clinically insane are another matter, but again, manufacturing an explosive takes time and materials, that means more chances to get caught. Plus it takes a lot of concentration and methodical procedure, or else you'll only kill yourself.
I know I'm sounding like an anti here, but I assure you I'm not. A gun is much more readily available than any explosive, despite what anyone says. We need to be able to recognize the weaknesses in our position, (and if you think we don't have any, you're dreaming), so that we can argue rationally.
That's all I'm trying to say.