There are a lot of irresponsible or air-headed people out there that, despite lacking a criminal record, I would hate to be anywhere near if they were in possession of a firearm.
Even if they receive training, it just doesn't sink in. Maybe it's a lack of common sense? Maybe some of them are just aware enough to know they shouldn't be handling/owning a firearm?
I quit a gun club where, after starting a weekly defensive pistol league, bullet holes started appearing in the roof and walls. Some members, despite years of experience and "training", couldn't get through a match without muzzle sweeping other members. There was more than one accidental discharge, too.
Would you feel safer knowing one or more of these guys lived in your town?
There's a lot of responsibility involved in just handling a firearm in a controlled environment such as a organized shooting range, let alone out in the general public while under duress.
I just hope that the people who do carry have very carefully considered the responsibility they have assumed and the consequences of a bad decision on their part.
It's not all "Big hero shoots the bad guy and saves the day"!