Remathilis said:
Alignment exists in the game for META-game reasons. That is, it is present in the game for the use and misunderstanding of PLAYERS, not the perceptions of CHARACTERS in-game. Thus it is difficult to assign any concrete tangibility in-game since it's purpose and effects are so oriented to meta-game issues.
2.) Magic is just a carrier
I assume this is a misspelling of
career.

Just because it exists in the PH, because it has clearly defined rules and is so frequently encountered, used and abused by Player Characters is insufficient reason to assume ANYTHING about the demographics of magic. Note well that the demographic information that is provided and inferred from the tables for generating communities in the DMG has clear, but virtually never understood or accepted caveats that the tables are for RANDOM generation of information about a town for which the DM does NOT have more data on and needs to generate facts quickly. It should NOT then be inferred that it is a wholesale replacement for or dictation of a useful world-spanning demographic system across multiple campaigns.
4.) Adventuring is the quickest route to self improvement: A farmer could spend years trying to earn the exact same amount of experience that a fighter does in one outing of slaying orcs.
Similar to #1, the experience point system in the game is a META-game tool. It is intended for PLAYERS to use to monitor and execute the improvement of their characters inherent abilities. It is intended for DM's to use to pace the improvement of player characters and by ASSIGNING experience points and levels, to DICTATE levels of skill of NPC's as well as their mere survivability in comparison to PC's. It is NOT intended as a logical system of IN-GAME self-improvement and comparison for the characters that inhabit the game world. The fact that the DM assigns an NPC sufficient experience points to be a 6th level commoner implies ONLY that doing so imparts a set amount of skill points and gives the NPC a given level of survivability - it is not a sign that the NPC has in the past, or will in the future, much less that he would/could/should EARN xp in EXACTLY the same fashion as PLAYER characters. The oft misread notation in the DMG indicates only that IF a 6th level commoner were to fight orcs that he WOULD earn xp as a PC does, not that this is how he must have gotten the XP he has or that it is the only method by which the DM can ASSIGN him xp in the future.
6.) Faith, Religion, and God is Real. Faith is not believing in some cannon of law or some abstract deity. The miracle of the gods is REAL.
As with assumptions about demographics itself this is predicated on assumptions that can't be dictated for all game worlds, whether the rules for this sort of thing are presented in the Core books or not. The fact that spells and magic items CAN allow travel to the plane of your future afterlife and direct interaction with deities simply cannot be taken as inference that such MUST have happened before, nor that it has happened to any degree that imparts a widespread understanding and undertaking of such activity, nor that it ever will.
Yes, it generally DOES mean exactly that but it doesn't HAVE to simply because it's possible.
8.) Magic is Everywhere.
...
All of these are paths of magic. To the commoner, they are practically the same, so it reasons out that you can gain power from ANYTHING.
Again requires assumptions that all of those types of magic MUST exist and that the theories and forces that govern them WILL be the same from one game to the next (even if the game rules don't change) such that inferences can be made about how knowledgeable a wide cross-section of a populace can be in a given campaign.
9.) Death is not the end.
This one too. Resurrection magic (Raise Dead, Resurrect, Reincarnate) exists in the game for PURELY meta-game reasons - for the continued play of PLAYER characters. I've never seen anyone even attempt to demonstrate otherwise, yet it is ALWAYS assumed otherwise in any discussion regarding the disruptive effect it has when applied wholesale across a game world. It has simply never been included to imply anything about its use by NPC's on ANY scale and it is thus a mistake to make inferences about what a D&D society would/could/should believe about the finality of death even though these spells exist in RAW.
For example, my own insistence is that upon their deaths, most NPC's find themselves in the afterlife that they desire and expect and thus it is EXCEPTIONALLY rare for an NPC to elect to return to mortality - even when they INTEND to before dying. PC's are exceptions, NOT the norm. This is a perfectly reasonable and even DESIREABLE assumption for NPC's given the RAW. Assuming that the mere possibilities suggested by the existence of resurrection magic MUST be carried to their utmost and makes death a highly impermanent state is HORRIBLY UNdesireable and a vastly disruptive approach.
Now before you rant on about how impossible something is in D&D, think on these ten "truths" as the people living in this world would see them. Its a very different world than the one you or I live in...
Well I hope I'm not ranting - and I'm certainly not trying to label any of the OP as actually IMPOSSIBLE. I just find them to be frequently undesireable conclusions based on false, or unnecessary assumptions. It is as a RESULT of thinking on these things as a person living in a D&D world sees them that I have reached many of the opposite conclusions that the OP presents. YMMV, but I prefer a game world that perhaps actually considers much of the PH, DMG, and even MM to be little better than speculation about its realities much less that it dictates to me basic elements of how my NPC inhabitants should view their reality.