Yes, but this is also my point. People seem to be treating Adventurers as if they're something the world hasn't had before or as if they have to be outsiders. There's genuinely no reason Bob the Farmer can't be a Fighter of some level and just much prefers being at his farm to going out in the world.
The "roman soldier who bought a farm" story, which is not "a tale as old as time" but is around 2,000 years old. I agree, some of the populace should have PC classes. Some PCs retired at some point.
I liked the 3e DMG because it had a framework for that, as well as for getting the less powerful NPC capabilities. While I suspect few people really used their demographics, the existence of those tables made a lot of DMs actually consider the demographics of their world.
Like, how does this kingdom fight off goblin hordes if there aren't a couple thousand people who can wear armor and use weapons effectively? How about the "ghoul marsh"? What priests do they have to drive off the undead?
As for social attitudes, I use all of the scenarios. Some villages were terrorized by adventurers and fear them with reason. Some villages fear them for no reason. In some cases there is jealousy or some kind of rivalry. Some idolize adventurers, or offer them lifetime discounts or even property. Same gamut for nobility and existing churches, mages guilds, bardic colleges, druid circles, etc, etc.
And I sometimes use all the scenarios at the same time and place, separated by groups/individuals so a locale can all have different views. (Commoners idolize, nobles fear, priests are jealous, wizards hope to trade spells, druids hate them, etc)
Eventually, some noble grants most of my games' adventurers lands. Often a couple days outside of town, near an area that is prone to having problems of the monstrous sorts. A "keep on the borderlands". Let them draw off the adventurous, excitable types as followers and you might cull both the monsters and the troublemakers in a win-win. This can be justified by a whole host of attitudes so even a craven noble ("monsters AND adventurers are scary!") can claim noble reasons ("for their heroic valor...") for granting lands ("....waaaay over there near the scary things where, {my deity} willing, they exterminate each other").