Your last statement regarding type of gun was a bit silly. This current one is up there but not so much as the last.
We all know this could have been avoided if the length of blade limit was 1 inch instead of 3 and certain types of knives were banned. Who needs a butter knife anyways?
The sad truth is that if someone has the will to kill others, there is very little to stop them. Hell, steal a dump truck and run it down sidewalks and you can do more devastating damage than a kid with guns in a movie theater.
I won't disagree with you that guns make killing more efficient. Regardless of that point though, with little creativity and intellect, one can create ways of mass killing cheaply and equally or more efficient. I'll not post any suggestions but I'm sure you can think something up.