I find that people that don't PLAY the classes don't get the same experience as someone who NPCs them. An NPC is not in every encounter, every game. PCs are. NPCs don't earn and use XP, they go up when you want them to. once again the problem is some people like mechanic that give them choices in and out of game.
You're assuming a lot. Our PCs don't earn XP either, we just level up after 4 or 5 sessions, or after the completion of an adventure module, and we've been doing this since AD&D 1e. So NPCs and PCs in our game level the same way, pretty much - when it's appropriate and at no other time. When my players level, my surviving NPCs level up to, and the exactly same way as PCs - there is no difference. Perhaps you don't have games with the same villain over 20 levels of play - we do this a lot, thus we gain the full experience of leveling up every given class, PC and NPC, as GMs. We don't wing it, we do it by the book.
I don't under stand why anyone would ever say that we shouldn't have our idea of fun... and saying things like "Broken book" or "Lotsof players don't like" or "I will never let it in my game" are all ways of saying "Badwrongfun"
Nobody did this - you're assuming again.
Nothing is banned in our game until we try it first. That's what play-testing is all about. Once tested, if we find something bad for our table, we ban it, plain and simple. However, just because something is banned at our table, doesn't apply to anyone else's game. I would never suggest what doesn't work for our group, might not be the perfect mechanic for someone else's game. However, is it wrong to ban a particular aspect of a game if it doesn't work for you?
I never said "that you shouldn't have your own idea of fun" (only you did). I don't judge your table, your accepted rules - so why are you judging my table's game?
Some definitions:
Broken Book
If a book is broken for anyone's personal game - it is indeed broken (as in the game-changing aspects of using a particular mechanic ruins the experience for our group). It doesn't mean it's broken for everyone's game, only the one we actually play in.
Lots of Players don't Like...
If every player you've ever met agree with a particular mechanic as being a poor one, wouldn't "lots of players like/dislike" be meaningful. I cannot say what the players I've never met have opinions on, I can only measure what I've witnessed. In my experience, every player I've ever sat a table with (even at our FLGS) thought that martial adepts sucked as classes and a general mechanic. It very well might not be true for every group, but I have no experience with every group.
I will never let it in my game...
I've never made this claim about any game mechanic. Every game mechanic that we include and exclude from our table was play-tested first at our table. We don't arbitrarily judge a particular mechanic as bad without trying it, so I would never outright ban something we did not test first. We drew up martial adepts for all our players, ran them through an entire module (well most of a module, since we all decided to hate Bo9S before we finished that module). We didn't just read the book and decide without trying.
I've never used the phrase "badwrongfun", so would never compare any mechanic with such a stupid phrase. However, if something doesn't work for your group - is it wrong that we don't choose to use a mechanic, as if you shouldn't be allowed to ban anything? I think martial adepts suck, but am perfectly willing to agree that it might be the most wonderful thing for you. Since you don't play at my table, I just don't care what works for you - that's completely meaningless for my game.