I came from SD and concealed carry permits were common there. Part of that is the utility of the permit in avoiding the need for a NICS check, a handgun permit, or any waiting period for a handgun purchase.
The regular permit is also very easy to get - $10 and a quick visit to the Sherriff's office s all it takes in most counties.
SD also has a very strict interpretation of "concealed". It is not concealed if it is UNLOADED and carried in a trunk or other closed compartment (and glove boxes center consoles do not generally count in this regard), or if it is UNLOADED and carried in a case that is too large to conceal on your person. Otherwise, you need a concealed carry permit. Sitting on top of the dash, or in plain sight on the seat = concealed. Sitting in a holster on your hip with a coat covering all by the bottom inch or so of the holster = concealed.
The end result is that a concealed carry permit is very useful, even for people who do not conceal carry for self defense.
In SD there are about 870,000 people, and about 95,000 concealed carry permits. When you consider that about 225,000 of the population are under 21 and are not eligible for a permit, the percentage of adults with a permit is around 15%, or about 1 in every 7 adults.
It's not all cupcakes and roses however, as while SD has a pretty active gun culture and teaching of proper gun handling is more common than in non gun culture states, you have a greater potential for untrained people and or the village idiot carrying a concealed handgun when there is no training or live fire qualification requirement to help weed them out.
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If you are an LEO in SD you recognize you will encounter armed citizens on a regular basis, even if only a fraction of them carry on a regular basis.
If you are stopped in SD for a traffic violation and you notify the officer you are carrying concealed, the response will most likely be along the lines of "just leave your gun in your holster and I'll leave my gun in mine". It's not big deal because they do it every day. If you're asked to exit the vehicle so the officer can confiscate the weapon, it's a signal that he's either new on the job, or he views you as the potential village idiot.
If you get pulled over in a state where concealed carry is uncommon, the officer will probably want you out of the car so he or she can confiscate the weapon. This creates all sorts of needless risks and safety issues, but the officer doesn't encounter the situation much and just doesn't know any better. If it makes him or her feel more comfortable , just roll with it.
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Now let's apply this to an active shooting situation in SD. Church, shopping mall, whatever, if it's not a gun free zone, the responding officer(s) know that there will be armed citizens present (and even if it is a gun free zone, they'll strongly suspect there will be armed citizens present anyway). It's just the norm in the area and they'll be anticipating the potential for an armed good guy. It's not regarded as a "problem", rather just something to be aware of and it's figured into the situation.
Take the same active shooter event in MD and you'll have officers who rarely encounter armed citizens and who do not know how, or have not even considered how, to respond in that situation. To those officers an armed citizen is a "problem".