I mean, of all the things I've heard players complain about, fudging doesn't even crack the top 10. IME, no one really cares. We all know that the DM has his or her thumb on the scales from time to time. That's just part of DMing.
@Vaalingrade isn't wrong pointing out that virtually every DMG in existence tells DM's that fudging when, in your best judgement, doing so would result in a more fun game, is perfectly fine and even expected.
The idea that if I change a crit to a regular hit, one time, suddenly no rolls in the game ever matter for all time, is ridiculous. As a DM, I'm going to roll hundreds or thousands of times over the course of a campaign. Ignoring the roll from time to time does not mean that the dice don't matter.