Let's be clear about something, the word "training" covers a lot of different territory, depending on who is using it.
For some people, it means some kind of formal / classroom instruction, only. For others, myself included, "training" is like "education". It includes, but is not limited to classroom instruction, it also includes ALL experience and familiarity.
Still today in the US there are a LOT of people who literally "grow up with guns". Daily carry and use of firearms for sport and agriculture is normal for many. And while there are a few idiots (which can be found everywhere) the majority of these folk know what they are doing, and do it safely.
The only real "training" these kind of folks need, or benefit from is instruction about their legal roles and responsibilities. They already know how to operate firearms, often quite well.
And that instruction need not be in a classroom setting to be both correct and effective.
Unfortunately, in the modern age, we have a lot of people who think the only way people learn anything is to learn it from a "certified instructor" and have some kind of paper to stick on their wall "proving" it.
For almost opposite ends of the spectrum, compare the enthusiastic "cilvilian" (or amateur if you prefer that word) who spends their own time and money, hundreds of hours, if not thousands or tens of thousands of hours over a lifetime, "training" with firearms, BECAUSE THEY WANT TO, against a police officer who has little interest in firearms, and despite wearing one every day, only "trains" with their arm for their annual range qualifications, and only does that because it is a job requirement.
Yet to the general public that police officer is assumed to be knowing and skilled, while the private citizen is not, UNLESS he/she has some paper from a recognized, "certified" instructor.
A curious double standard, but a real one, nonetheless...