Do you think unrestricted carry was popular and widespread throughout the 20th century compared to today?
Depends on what region of the US, I suppose, but around here,
definitely not. And I live in a so called "red state" that has been so for generations. I was born in the late 1950's, and respectable middle class/working class people
in these parts rarely, if ever, carried back then, as far as I know. I remember in the 1970's my cousin and her husband from Chicago came to visit, and (according to my dad), a .38 revolver accidentally fell out of my cousin's husband's coat. My parents were horrified that he was carrying a concealed handgun, even though my dad was a gun owner (enthusiast, even.) The problem was that my parents couldn't understand or relate to what living and surviving in some parts of Chicago - or any other big city - was like. It wasn't until the violent crime rate started going up drastically in their own moderate sized city (and even immediate neighborhood) that they started to realize what was going on.
I personally don't believe that the concealed-carry movement that swept the country 20-30 years ago was motivated by the second amendment
specifically among the general public, although the principal was certainly embedded in there somewhere. In other words, I don't think most Americans were as constitutionally minded as the NRA or other gun advocacy groups. I believe the movement was a result of a drastic rise in crime in major cities, as well as what you might call a "culture of lawlessness" among inner city gangs that were responsible for a significant amount of that crime. (As I recall, it was Miami where the CCW stuff started, and Miami was like the most violent place in the US back in the '80's.) Eventually, that sort of crime started spreading to a whole lot of other places (like where my parents lived), and most states and municipalities had to acknowledge the inability of state and local police departments to keep people safe.
So, like others who have posted on this thread, I was against CCW legislation at first because it wasn't part of my cultural experience; I didn't grow up that way, even as a conservative. But then, over the span of several years, three acquaintances of mine - and one neighbor who I never got to meet - were all murdered in separate instances by strangers who had no history with them. No "drug deals gone bad" or "domestic disputes"...these people were all just out in public minding their own business. One was a gang murder. Another may have been. This was all in my midwestern conservative state. That's when I started entertaining the notion that the Second Amendment also includes protecting one's self in public. If you can use guns to defend against a tyrannical power or government, as the Second implies, then why can't you use guns to defend yourself against tyrannical individuals? Makes perfect sense, and the legal scholars and judge's concur, thankfully, thanks to the NRA and other groups.
Do you think that explicit permitting of carry has increased its practice?
Around here, definitely yes. Even more so in nearby states.