I agree with you in theory. If every law abiding citizens carried a concealed firearm an knew how and when to use it without lapses in judgment, then violent street crime would ebb to a trickle. But then there is reality. In this particular case, all of the victims were on the way home from a bar after several hours of drinking, which probably explains why the dead woman mouthed off to the killer. Let's assume they were intoxicated, which is probably a pretty good assumption. If one or more of them had pulled a weapon there a pretty good chance they would have screwed up and shoot themselves or an innocent bystander, prompting the intended target to open fire on everyone and instead of one dead criminal, we would now have several dead victims.
Well don't take it personally, but it's pretty hard to screw up more than winding up dead. I recognize your points, but not everyone exiting a bar is blitzed.