I just see fudging as fundamentally refusing to play fair. The numbers are meaningless, the rules are meaningless. Nothing I as a player choose or attempt truly has any weight. For literally whatever reason the DM thinks is justified, the world can and will warp around their new concept. I will never be allowed to know how things actually worked out. My tactics and strategies always and eternally have the giant asterisk of "assuming the DM actually plays by the rules." Even if the DM never, not even once, chooses to do things that make life harder for me (such as adding HP to a boss, which is literally exactly the same as taking away damage from previous player rolls), they're still denying me the ability to earn my victories and learn to play better. I'll never truly know, and thus never truly he able to trust, that I succeed because I perform well; if it's hidden from me (as most advocates STRONGLY recommend, to the point of "never EVER tell your players you fudge, literally actively lie to them to conceal it") then I'm actively being deceived, and if it's only soft hidden, as in the DM admits to doing it after the fact but not while doing it, then I'll never really be able to feel like I'm playing a game. It will always feel, at root, like I'm being pulled through the DM's novella and any victories I earn are just what story beats she needed to tell.
That's why I cannot accept any form of fudging. If it's secret, it's unacceptable. If it isn't secret, as in, if the players can actually find out in the moment that it is changing and either respond immediately or learn how to respond in the future, then it's not fudging, and I have no problem with it.
I expect every DM to play fair. That means either playing with your cards face up (no concealment at all), or giving me the chance (even if it ends up not working out) to find out what the cards are. Anything else is not playing fair; it would be pretending that there are rules and limits, and then breaking those rules and limits whenever and wherever you feel like it.