Its a law for ATVs, Cars... I seen too many scary things at many ranges with accidental discharges by self taught individuals. Saw one yesterday, an individual had a misfire and tried to open the action with the finger on the trigger and discharged 15 degrees away from the backstop. Imagine if that happened elsewhere? It doesn't have to be an NRA course. Just some basic understanding of the firearm and the big 3 rules is a good start.
But should it be government mandated, or the individual's responsibility? I believe it is the individual's responsibility to learn and handle their firearm safely. If they have an ND in public, prosecute them for the mishandling, but don't assume they're stupid and need their hand held and REQUIRE training. STRONGLY RECOMMEND training, yes, REQUIRE training just to own or even carry, no.
If someone with no firearms training or a million hours of training acts responsibly with their firearm, the gov should butt out. If someone with a million hours of intensive firearms training or no firearms training mishandles their firearm then the gov should step in and prosecute that offense. The gov's job as I see it is to define and prosecute misconduct, not attempt to legislate stupid away cause that's just not gonna happen.
Someone with no training is probably more likely to have an accident than someone with lots of training, but I've heard of many people with LOTS of training having Negligent Discharges almost as often as I hear of people with NO training having ND's. I realize that probability of an ND goes up the more you handle a firearm regardless of your amount of training, and someone who trains often is most likely going to be handling a firearm much more than someone who does not train. I also realize the value of training and that more training usually makes you a safer gun handler. However, that is a big USUALLY and doesn't apply to all cases or all people.
I guess my Libertarian views are coming out. I just don't think it's the gov's job to tell me how to handle my own affairs unless I do something bad that affects another person (ie. a ND in public). If I'm capable of handling a firearm safely with no formal training because I learned it from my dad as a young child, and I go through my whole life carrying every day and not hurting anyone or acting irresponsibly, then the gov has no business telling me that I need to spend $50 or $100 or more on a class that I probably know more about than the instructor, just to get a piece of paper telling me I know what I already know.