P: As the GM, I should fudge rolls.
R: No. Fudging rolls is lying and antithetical to the nature of RPGs.
P: Fudging rolls is like bluffing in poker, not lying.
R: Laughably untrue. In poker your bluff can be called and you can safely show it afterwards. In tabletop, on the other hand, players aren't allowed to call the GM's bluff, and as a GM you can never admit to your players that you fudge at all, let alone which rolls in particular, for if you do, you lose their trust forever, just as if you had lied to them... because you did.
P: Fudging rolls makes the game more dramatic.
R: False. Drama comes from genuine risk. If the GM dictates the outcomes, there is no risk.
P: Fudging rolls makes the game more entertaining for the players.
R: False. Player agency and a consistent world are the central draws of tabletop RPGs. If the GM arbitrarily decides outcomes, players are robbed of agency and the world loses consistency.
P: Fudging to save a PC results in more fun than letting the dice kill him.
R: It only seems that way in the moment. In the long term, losing a character to the dice is more entertaining than ceasless 'close calls' and trite 'dramatically appropriate' deaths; furthermore, it teaches players the value of caution and planning ahead.
P: My player won't have anything to do for the rest of the session, or even the adventure, if I don't fudge to save his PC.
R: Every player should have at least one backup PC ready to introduce at the earliest opportunity and the party should have followers/hirelings for the player to manage. It is rarely diffuclt for the GM to find a reason for a new PC to arrive.
P: My player will be sad if I don't fudge to save his PC.
R: Get a different player or play a game where the stakes aren't life and death.
P: It sucks when a random crit kills a PC at the beginning of a battle, so I should fudge to prevent that.
R: Instead, play a game with player-facing mechanics to prevent untimely deaths (bennies in Savage Worlds, Luck in GURPS, etc.), or play a game with weaker crits, or play a game where death isn't on the table. There are many options that don't reuiqre lying and arbitrarily overriding the rules.
P: Fudging rolls makes the game more entertaining for the GM.
R: False. Truly unexpected outcomes are more entertaining than making the players act out your script.
P: Every GM fudges rolls.
R: Patently false. You can find people all over the internet talking about how they roll openly and always have.
P: Gygax/AD&D said fudging is the GM's perogative:
P: The players won't notice.
R: They will, and once they notice, their trust in you will be gone forever. After every close call they will always have that doubt lurking in the back of their minds: "Did we really succeed or was it just GM fiat?"
P: No, really, I'm a good liar. My players will never notice.
R: I don't believe you. There are always tells. Even supposing you were right, it would at best mean your players are brain dead.
P: Building the setting and NPCs is just as arbitrary as fudging rolls.
R: As creator of the world the GM is necessarily arbitrary away from the table, but at game time he is a referee, with all the impartiality that implies. Moreover, arbitrary though they must be, the setting and NPCs are mere starting points, not outcomes. There are often ways for smart players to overcome or avoid even overwhelming obstacles, but there is no recourse for players when the GM begins dictating rolls.
P: The GM must fudge to keep the game on course.
R: There's no such thing as 'on course' because tabletop RPGs aren't novels or plays. If you, as the GM, have an unalterable 'course' of events planned out in advance, you should be writing a book instead.
P: It's ok to fudge if I do it rarely.
R: If you fudge any roll they all become fudged, in a sense, because you accept the idea that only outcomes of which you approve will be allowed to stand.
P: There's no right or wrong way to run a game, so don't tell me not to fudge.
R: If your players like knowingly LARPing your novel, more power to you. It's still lying if you pretend that's not what you're doing, though.
I won't respond to any post raising points already addressed here.