I don't think you've really been following the case much.
First off, before James started shooting everyone - he set off two homemade canisters of what could be best described as tear gas. Definitely a few of the 70+ people they are now treating in the hospital are being treated for chemical type lung issues due to this gas.
Second, he booby trapped his entire apartment complex with both chemical and incendiary devices which are probably home made and capable of causing a huge bunch of chaos. Destruction, fire, who knows.
So if guns were illegal, what would have stopped him from blowing up shit instead, he might have even killed more people a la Timothy McVea and the Oklahoma city bombing. He could have just drove his car into the theatre, got out and boom.
So where do you draw the line? So lets assume we outlaw guns, then what? James can't get that - that's naive first of all as you said yourself - our culture is saturated to the brim with them as it is, and even if we were to put a complete halt to all manufacturer and sell of guns in the US, and imported to the US - how many are already here? How easy are they to get? Who knows, but I am willing to bet it will be as easy as weed, or prescription drugs, or even heroin.
So. ....
Lets assume its harder for him to get the guns then. Shit the fucker goes out and blows up the whole theatre, then what? Ban fertilizer? Ban all the different substances we can use that can make explosives or chemical weapons of any kind? Where do you draw the line?
Your pissed and I get that. But all of you anti-gun freaks that show up at times like this really piss me off too. It can't be done. Guns are a part of AMerican culture unlike any other culture in the 1st world and its just the way it is. Its like trying to stop the whole internet now that it has become what it is. Its not possible so you need to sit down, rationalize and try to come up with remedies that help the problem. Not some dimwitted, half assed response that wreaks of the prohibition or the war on drugs. Which did a whole lot to stem the flow of alcohol, or the tide of drugs into the country, let me tell you!!!
How many jobs would be lost if we got rid of guns? Would cops not carry as well a la the UK? WOW. The mess I could see resulting in America if that were to happen, Anarchy on the streets is all I can see. Honestly, I'd like to see it happen just because I'm a vindictive asshole and I'd like to tell assholes like you that I told you so. Any legislation that was passed would be overturned so fast that it would make prohibition look like it lasted an eternity.