This article is seven years old. For those interested, I upgraded my opinion about this question a few months ago, as I am always evolving as a DM.
Here was a stunning assertion from runjikol, in reference to the statement that NPCs are props for the game, made in the comments section of the previous post:
"PCs are just props for the game, too. They're the props of the players. NPCs the props of the GM. My point is that the internal rules of the game, when it comes to mechanics and what can be achieved with them, I want to be consistent between NPC and PC. So if a PC can sway an NPC with a Charisma check then an NPC should be able to sway a PC with a Charisma check, too."
Let me make something clear. 'Non-players' are NOT players. NPCs are not characters through which the DM 'plays' in the campaign. The DM who uses NPCs in a way so as to feel a part of the game is seriously deluded about the DM's role.
I hate the term referee where it is applied to the Dungeon Master, mostly because I like that the game has independent terms, applicable only to its own milieu. But 'referee' is a helpful term in this circumstance. Referees are not players, and are subject within the game to rules that apply only to them. Referees are never allowed to touch the ball. Referees are not allowed to change, influence, or otherwise stymie the course of play. They are not privileged to exercise their emotional judgment in a given circumstance. They are highly discouraged from interacting with the players of the game, even in regards to friendly banter. The referee does not answer when casually addressed. The referee does not offer casual chatter or advice. The referee calls the game, and that is all.
So when I hear the NPC promoted to the level of the PC, so that the referee can play along with everyone else, the spines along my back rise, my breath shortens and small animals nearby ... mildly take notice.
I realize that DMing can seem lonely. I generally feel a bit down after a campaign, worried about whether it went well, if everyone had a good time, or if the ideas I presented just sucked. Sometimes, I know that they did. And those times paint the good times with a sort of "I'm not sure if they're being polite to me, or if they had a good time" kind of vibe. Only now and then do you have a session where everyone is so ramped up that there can't be any question about the night being kick-ass.
In fact, the after 'drop' of DMing a game is similar to performing on stage. Prior to the performance you arrive at the theatre, you chat with others, the stage manager makes a few announcements about ongoing technical issues (the director has long since departed for better shores), and the level of energy is still quite low. But as people move around getting their costumes together, as you have your make-up applied, as the props that will be wrecked during that night's performance are brought forward from the rear shop, and as things are flipped on and tested, the energy level climbs. The doors are opened, the audience starts to mill around the lobby, the voices in the back are hushed and ultimately suppressed completely ... and at the point when you are frozen in place, ready to go on stage, making the least movement possible so as not to give yourself away, your skin is flowing with electricity. Most of the cast feels their nerves take hold. But then the play begins, and you walk the boards, speak your lines, insult the designated villain, pontificate about the verisimilitude of life to earn whatever applause you're due that night, and the energy tapers off. The play is over. You bow, you walk off stage, you scrape the make-up away, throw off the clothes - some to the laundry, but most not - and you're done. There's no cast party in a run, but someone is always ready to get drunk ... because, you see, with the performance over you feel like absolute shit.
The energy has gone through you and you are now a dead battery, dry until you're powered up for the next performance. The experience is different for you. You were not a member of the audience, sitting out front enjoying the play. The play for you is work.
You might catch a snippet of pleasure watching someone you like perform their bits, but probably not - you've got your own character to get into, a character over which you have NO CONTROL. It does what the writer and the director have agreed upon. Not you. Your performance is to behave in a manner that makes the other actors more comfortable from night to night. The last thing you want to do is act like an idiot, forcing the play in the direction you want it to go, since that will only destroy the creator's vision. You are not the creator, you are the facilitator. And however well you've facilitated, when it's over, you're left feeling like shit.
There are DMs out there who delude themselves into thinking they write the play, or that they direct the vision - but they're wrong. The dice write the play. The dice determine the winner and the loser. The game has designed the sets and built the stage, and brought in the audience. All the DM can do is perform the vision as well as he or she can, take a bow, and - with luck - not have to get tight alone afterwards.
Now I realize I've put two metaphors forth - DM as referee and DM as actor. I've been careful not to mix them, but to present them in order. As the gentle reader reads, please try not to mix them up. A thing can have more than one metaphor applied to it. A thing often has better than only two. A complex thing might need seven or eight dozen. Try to read each metaphor as though I gave it independently - which, in fact, I did.
And when you DM, and you're fucking up trying to be both the audience and the performer, or trying to be both the player and the referee, try to note the dull, unhappy faces of your players and recognize that they're blaming this particular presentation on you.
You may only be the facilitator, but unfortunately for you, you're the responsible facilitator. You wanted the part. But that doesn't make you more important than you are. The players came to PLAY. You're only there to perform.