...Why with all these options available to him why did Cho Seung-hui choose guns not fertilizer based explosives, or his hammer, or a knife or a toothbrush? If someone pro guns, could provide an answer to that I would be very pleased to know...
Stupidity? Mental instability? Paranoia? Chemical Imbalance? The guy was a complete and certifiable whack-job. He mailed a video, pics, and rants to NBC before he went off, outlining his intentions and "manifesto". This is not someone who randomly picked up a gun because it was convenient and managed this amount of carnage because of the weapons he "stumbled" upon, it was pre-meditated, thought out, planned, and staged. The short answer is that the guy was just plain crazy. I would not be surprised if someone as disturbed would have attempted to kill people with a used condom and a soup spoon
There was an incident of road rage in MD last week that escalated from the usual one-finger-salute to vehicle-A pulling directly into the path of vehicle B and locking up the brakes. Vehicle-B swerved, flipped, went off the road and into a patch of trees, killing both occupants. Obviously, the car was not intended to kill people, but in this case that's exactly what it was used to do
It does not mean the car, manufacturer, or dealer are responsible for the actions of the driver.
I think you should also temper your argument with the distinction between "pro-guns", "gun-control", and "gun-ban". Despite what the local misanthropes might lead you to believe, the general consensus of American citizens is
NOT that guns should be freely available to anyone at anytime, but that their purchase should be controlled and examined and that complete background checks should be completed prior to sale (which did occur in this case, btw). You also need to understand that what is more frightening than the stray nutter that slips though the cracks and obtains a gun is any government that fears weapons in the hands of it's citizens.
Which leads us back to my original argument that you so conveniently ignored... it is not the guns, it the person. Fix the person, the gun argument is irrelevant.