There is a pretty good test to see whether or not someone is responsible enough to exercise their right to own and carry a firearm. How do they handle and conduct themselves in other areas in which there is a measure of danger or potential maleficence?
For danger, we have driving a motor vehicle, operating power tools, engaging in dangerous sports with reckless abandon. etc. Doing any of these activities which show a callous disregard for one's safety and that of others is evidence of questionable behavior.
For maleficent behavior, we might include a propensity of heavy drinking followed by violent activity (looking for fights), drug use, volatile temperament, and similar traits.
So if you are riding with a friend who is considering getting a firearm to carry for protection and you note that he speeds, darts in and out of traffic, runs lights and stop signs, shouts profanities at other drivers, and displays behavior that leaves you uncomfortable in his vehicle, do you really want to see him carrying a firearm? If you go out to a restaurant and he wants to stay at the bar and drink then gets angry and makes comments to other patrons who notice his behavior, do you think it's a good idea that he might be carrying a firearm soon?
One's behavior, how they conduct themselves in general public surrounds, says a great deal about their mindset, their maturity, and their responsibility factor. I used to go groundhog hunting many years ago with two guys who one day showed up acting "strange". Come to find out they were both high on killer weed (mixed pop). I never went out with them again. No way I wanted to be around people like that with loaded firearms.