I’m sorry to hear the guy was gunned down in front of a courthouse, but that isn’t exactly a gun-free zone. The fact is, a lot of gunmen are opportunists, and there’s no possible way you can defend yourself - with a gun - every moment of every day. It isn’t like every shooter announces their intentions ahead of time, so you can prepare.
The NRA’s wet dream is an epic fucking shootout at any given moment. The problem is lots of the wrong people can get shot that way. As this carry-at-all-times hysteria escalates, that’s exactly what will happen. And chances are, the target(s) of the shooter will already be taken out before it becomes a shootemup involving armed onlookers. So what has that accomplished?