I totally disagree with the mastery part. As long as someone can practice good gun safety, that's all I care about, and even then I don't REALLY care if Joe Schmuck is 100% safe. The rules of CCW mean Joe Schmuck is never going to be handling a gun in proximity of me unless in a rare case where I'll probably be at least >50% glad he at least has a gun. Only other scenarios where I'd be near him while he's handling a gun:
1. he's illegally brandishing
2. we're at a shooting range, where CCW doesn't matter, anyway.
3. we're in a private residence where he's playing with a gun. I.e., I'm friends with this idiot, and that's MY problem.
As for marksmanship, I also don't care. If Joe Smuck is shooting into a crowd of innocent people, that's a judgment issue, not a "gun mastery" issue. If he empties a 15 round magazine at an imminent threat and misses most/all shots, then he's still on par with the average police officer! And consider that in a scenario where someone needs to defend themselves with a gun, 99% of the time they're alone, to begin with, which is part of the reason why drawing is justified. There's little reason to think you'll ever need to defend yourself with a gun in the middle of a crowd of people. Some may daydream of being the "sheep dog" that saves the mall full of grateful citizens. But most people carry to protect themselves and their family, only. And even IF that scenario occurs, think about it. Wouldn't you prefer if someone had been carrying at Virginia Tech, even if they were a bad shot?
Also consider this. Do you want criminals in your area to know that any layperson might be carrying, including granny with the cataracts and the shakes? Or that just an elite few are allowed the privilege?
The key here is judgment. You can't test judgment. Like there's no way a drivers test is going to stop the few bad people who will end up driving drunk/recklessly/road-raging/road-racing as soon as no one is watching.