If you do decide to purchase a firearm and get licensed for that reason, may I suggest very strongly two things: go to a pistol range and practice, practice, practice your marksmanship, and mentally prepare yourself to do the thing which you are contemplating. If you are not mentally prepared, you will either hesitate or freeze and accomplish exactly nothing.
Also, be aware, that even if you do purchase a firearm and get your CCW permit, the odds are you will never, ever need it. You have a better chance of being killed in an auto accident than being involved in such a shooting. You should also be aware that the mall shooting, as do most such shootings, occurred in a “gun-free zone”. As a responsible CCW permit holder, you would not be armed in that building anyway.
Words to take to the bank. If you wait to figure out what to do in an emergency, it's too late. I know, I've been in a few emergencies, not with guns, but other dangerous situations such as small boats in storms.
The rule certainly applies to driving. What should you do if a small animal runs out in front of your car? What should you do if the guy coming toward you on a two-lane road goes into a trance and starts drifting over into your lane?
One of my sons totaled a truck last summer and almost got himself killed, because a hedgehog strolled out in front of him. He automatically steered around it, and as a result ran off a dirt road into a ditch and a tree. So, which is more important, the life of a man or the life of a hedgehog? And what if you can't afford a new truck and you need it for your work? Better to consider such questions before they occur.
You left out a step.
“go to a pistol range and practice, practice, practice your marksmanship, “
One of my pieces of advice for new shooters that are a little nervous, is that after the basic training, shoot a couple of hundred rounds, shoot until you are sick of shooting, shoot until your hand is sore and the pistol is totally demystified for you, and then get someone to show you how to do a thorough cleaning of it.
Make that pistol yours, load it, unload it, draw it, clean it, strip it of any emotional baggage, see it for your warm, good friend that it is.
Actually, you probably wouldn't even be IN most of those buildings.
If a property owner wants to put up signs saying "TRAINED, LAW-ABIDING CONCEALED-CARRY PERMIT HOLDERS NOT WELCOME HERE," then screw 'em. They're not worthy of your business anyway.
And they can deal later on with the massive civil liability lawsuits when some maniac takes 'em up on the welcome mat, and comes in their cute little "gun-free" zone and murders and maims their customers.