2) Adventurer does not exist as a profession, and societies with lots of individual freedom are quite rare. Governments do not tolerate armed bands of vigilante groups; noble rank is required to own a sword, licenses are required to transport weapons between jurisdictions, persons found on a lord's property (most of the landscape) with weapons without papers will be assumed to be bandits. An average person will not have heard the term adventurer. If you explained it to them they'd scoff and say, "Oh, you mean you are a blood soaking mercenary. Be off with you." The only case where you would here the term would be a mercenary joking about himself; like a pirate calling himself a 'gentleman of fortune'.
This quote of Celebrim's brought an interesting question to my mind
In a world with Normal D&D magic fuedalism and other primitive authoritarian systems of government really shouldn't exist IMO
Lets say you have a basic fuedal state (a protection racket really) how would you maintain it in the face of Clerics, Sorcerers, Bards and Druids
Ok you can regulate Wizards (spellbooks suck) but the other classes are well above the authority of any fuedal system
Lets take Clerics as an example, these guys get their power directly from Gods.
Unless the gods are either oblivious or don't care do you really think that any good being would approve of a system as exploitive as Feudalism.? I don't
Remember Clerics have spells like this (from the SRD)
Commune
Divination
Level: Clr 5
Components: V, S, M, DF, XP
Casting Time: 10 minutes
Range: Personal
Target: The character
Duration: 1 round/level
The character can contact the character's deity—or agents thereof—and ask questions that can be answered by a simple yes or no. (A cleric of no particular deity contacts a philosophically allied deity.) The character are allowed one such question per caster level. The answers given are correct within the limits of the entity’s knowledge. "Unclear" is a legitimate answer, because powerful beings of the Outer Planes are not necessarily omniscient. In cases where a one-word answer would be misleading or contrary to the deity’s interests, the DM should give a short phrase (five words or less) as an answer instead. The spell, at best, provides information to aid character decisions. The entities contacted structure their answers to further their own purposes. If the character doesn't focus on the conversation, discusses the answers at length with other parties, or leaves to undertake another task, the spell ends.
XP Cost: 100 XP.
Ask Questions like "Is this system of governence the best one to bring my flock closer to you?"
or "Is it right to disarm people"
I don't know about you but I don't want a god mad at me. Also the simple expedient of refusing to heal memebers of the noble family in the line of sucession is very effective
"Sorry your majesty but your acts offend my god I will not heal you or your kin"
Try and hold him and enjoy the benfits of a contagion spell unleashed on your Knights (or their might steeds hehehehe)
I suspose you can Inqusistion all the Sorcerers and Bards (relying on your Wizards to protect you) but if you do you you had better get them all.
People want revenge and a high level Sorcerer has access to unfathomable power. Lets say the Sorcerer whos mentor you killed wants revenge, he is about umm 12th level
He can probably do a number of the following
Convince you subjects to kill you with a few words
Deflect Arrows
Deflect Blows
Turn into a monster that can kill your knights
Burn the fields
Move anywhere he wants
Ruin the weather
KIll many of your warrior with a word
Summon things to fight for him
Bore a tunnel through any mountain
Your warrior haven't got a chance without magic of his owen
If you want scary
Imagine an epic level Sorcerer with a lightly modified Rain of Fire. Everything in a 2 mile radius is destroyed within an hour (1 pt of dmage per 6 seconds, normal people die in 30 seconds)
This guy can appear anywhere he wants, hit whatever he wants. You might get him eventually (assuming you can find him in his scry guarded lair) but not before he destroys, well everything
Druid and to a lesser degree Rangers.. Well if they don't like you,
well here is simple tactic available to a 3rd level druid or an 4th level ranger
"Speak with Animal"
Hey Pigs, did you ever wonder what happened to all your brothers and sisters? Well the humans here pin them , fatten them and slaughter them. Just thought you would like to know. I will leave they gate open on my way out...
When the swineherd comes into the woods -- He is eaten by a Grue

Stealing the sheep or pigs from a bunch of villages would decimate a fuedal economy
and if there are systems of which the gods do not approve, well they won't stand long....
I rather imagine this scene
King Henrik the Cruel glanced at the sheaf of paper before him "Vizier what is this report I here of uprisings"
"Well your majesty, there is famine in 2/3 of the villages"
"What?! How can this be"
THe Vizier swallowed, he had no desire to joing his predecessor in a crows cage "A band of so called adventurers milord, outlaws really
The king was surprisingly calm "Explain"
"Remeber that thief you had killed last year, the one they called Kilbrick Knifeshadow"
THe king though a moment "I think so"
"Well they want revenge and they won't settle until you and every noble is dead. They have attacked the very fabric of the lands, released animals -- burned crops --- attacked knights"
""Can't you stop them"
"My Wizards are trying Majesty but there are limits. We lack the resources to heal the men properly. After the incident with the Clerics, well...."
JMO but I really doubt people who can kill with a word, contact other planes and talk to gods will be easily controlled. Given the number of uprisings in the real middle ages I dsuspect all high level PC's would have to be soopted into the society (hope they aren't Chaotic in aligment) or destroed to make any authoritarian state work
As horrible to contemplate as it is high level character are super empowered individuals. If they decide to use terror tactics (very very common throught history" they can inflict destruction on a massive level. Think of them (in modern parlance) as super empowered individuals
A party of 4 Characters Ranger, Rogue, Sorcerer and Bard is unstopable by any lesser force. Throw in a couple of more maybe a Druid and something else and you kingdom is in for trouble
In a world where people like this exist other systems would work better Manocracy (governmnet by mages) Imperial States (if the government trains spell casters) Theocracy (obviuosly and likely a rather common form of government) Mind Control State or maybe even a Republic I don't think dictatorships, heridatary aristicracys fuedalism probably would work