The point of my comparison to stage magic is that even though the stage magician is pretending that something that is not true, is true (which is normally an ingredient of deceit), the magician is not setting out to deceive the audience - in fact, the audience knows they're being fooled, but they are willing to play along.
Of course the stage magician is setting out to deceive the audience, which is not necessarily willing to play along but who accepts that they might indeed be fooled, while at the same time just enjoying the show. There is absolutely no difference with what a DM might do, because in all cases, it's for the fun and entertainment of the audience (and the stage magician needs this badly because if the audience does not have fun or is being made fools, they won't like it and will not come back, just as if there is no "magic").
And exactly like stage magic, the audience knows that they are possibly being fooled, but they don't know when, how often and certainly not how, which absolutely fine as they are indeed playing along. I'm sorry, but you can't call what a stage magician is doing anything else than deception.
So IMO you never need to deceive your players. Like the stage magician and the audience, they can know they're being fooled and be willing to play along all the same. (And just like with a stage magician, it's not strictly necessary for the players to know how your tricks work.)
The stage magician needs to deceive the audience, it's the basis of his job, because magic does not exist in our world. Now, it's up to you, but if I want my villains to be real geniuses, for example, I will have to use some tricks for that, because I don't think I'm an evil genius myself. So no, if you play D&D as a combat game, there is need for that. If you play a complex game of intrigue, then it becomes quite necessary.
So what matters isn't whether you fudge or don't fudge dice, whether the ogre is "quantum" or not, and so on, but your intentions and the players' intentions going into gameplay, your gameplay preferences and the players' gameplay preferences, player buy-in, and how it all fits together.
There, I completely agree, what is a problem for me is when some DMs who play in a certain style absolutely need to label things like railroading, deception, fudging, etc. as bad things. To each his own, using the tool just before does not make one a "bad DM".
IMHO, what makes a DM a bad DM is when a DM is taking decisions with something else than his players' fun in mind. After that, a good intentioned DM might be awkward, or too transparent, or just a beginner, or unsure of himself, or less comfortable with improvisation, but it doesn't bring anything to anyone to call him a bad DM.