Note that playing a Red Court Vampires are one of only a few character concepts specifically not allowed by the RAW:
PS: I regard the statement about RCVs being invariably NPCs as a writer error.
In the fullness of the canon, and in the context of the basic premises of the game setting, the comment about RCV's becoming unplayable NPCs is an accurate (or at least a very defensible) statement. It gives poignancy to the danger of fighting RCVs, the possibility that one could become one of them, and in so doing, turn bad. They have done their best to set it up as a problem, and a serious threat for Red Court Infected.
In the fullness of what gamers would want to do, however, the writers could perhaps have opted to say "almost invariably," but that could (would) have opened up more questions, possibly inspired a thread about who the "good RCV" is that Jim Butcher is hiding behind the GM screen. Certainly a subculture which has been exposed to "Buffy," "Angel," "Vampire Hunter D" (and any number of other fictional depictions of vampires) would posit the option of playing a "good" RCV. And there are plenty of others who would try a Group Template which could accommodate an evil RCV.
So I take this statement as the "rule 0" answer:
YS72: "Regardless, while the choices listed here are hardly the only ones available in the Dresdenverse, they represent what we think are the best options for the would-be heroes of your game world. Enjoy! "
Basically, there are setting components which are fairly cut and dry, no mater how much someone wants to circumvent it or create the special snowflake character who is the exception to the rule:
Wizards hex tech and must thereby go without many modern conveniences.
Red Court Vampires are irredeemably evil and can't be "saved."
But each table gets to play its own game. People are encouraged to hold to the canon, but are free to make changes, for the sake of fun. Because if it's not fun, why do it? So long as everyone empathizes with those who *do* care how canonical their game is, it will be easier for those defenders of the canon to relax, empathize with and support those who do otherwise.
And I close with this:
Playing a Game in Canon with the books
Real Men: Respect the GM's wishes, but don't let it interfere with gameplay.
Real Roleplayers: THIS GAME MUST BE IN SEAMLESS CONTINUITY OF THE DRESDEN FILES AS PRESENTED BY THE ALL-FATHER, HIS HOLINESS JIM BUTCHER AND HIS PROPHETESS PRISCELLIE.
Real Loonies: Will take every opportunity to break the canon... whilst using cheese.
Real Munchkins: Will twist the GM's arm by keeping canon... only if they are the one that killed Simon Pietrovich.... or Kemmler.