This will seem sick and insensitive, but let's be thankful the Aurora shooter only had guns. Imagine the carnage if he had his PhD in neuroscience before pulling a Joker and wanting to "see the world burn."
This is one of the things that does worry me. Technology is progressing in leaps and bounds and it's only a matter of time before someone cooks up a virus or toxin in his or her basement lab. Actually, I think it's a testament to the goodness or laziness of mankind that it hasn't happened on a wider scale by now.
Two other thoughts: I hope the "humans are a cancer on the Earth" types start getting their due attention. I fear them more than I fear Islamic radicals, Christianists or the Tea Party. Second, all those James Bond movies where the villain is plotting the end of millions don't seem like fantastic escapist fiction anymore.