Explain to me again why gun ownership is a good idea

Local gun nuts are doing the happy dance because Georgia's new concealed carry law went into effect yesterday. I am not as sanguine.

Case in point:

Builder faces murder case:
Victim mistaken for copper thief, says Coweta sheriff.
Defense attorney says suspect didn't mean to shoot.

Just how stupid does a person have to be in order to not recognize his own subcontractors? And whatever happened to the idea of calling the cops if you think you're seeing a burglary in progress?

I'm not really in the mood to argue the Second Amendment. I do, however, think the key word might be "well regulated." I'd like to see that interpreted as "You want to own a gun, first prove you're not an idiot." I.e., be willing to sit through a waiting period and submit to a background check, take gun safety classes, and generally demonstrate you're a rational adult. If the Supreme Court is willing to concede that government has the right to keep guns away from criminals and the insane, I surely don't see anything wrong with trying to keep them out of the hands of the terminally stupid, too.

Update: a link suggested by Mathman: "A Tale of Two Amendments" by Matty Boy over at Lotsa 'Splainin' 2 Do. It got me to thinking that maybe the key to gun ownership should be being required to prove you're qualified to be a member of that "well-regulated militia." Army recruiters reject would-be enlistees every day; if someone isn't qualified to serve in the regular military, why should he or she be allowed to possess a private arsenal?