The Isaac community is surprisingly divided on this issue, because Repentance is unique in its difficulty.
The Purist Argument: "The struggle is the point. Dying on a Tainted Lost run to a spider because you forgot Holy Mantle is what makes the eventual Dead God feel valuable. An editor devalues the art."
The Practical Argument: "I have 1,000 hours and have beaten Delirium 50 times. I refuse to do Greedier Mode with Jacob & Esau because the character design is objectively bad. I use an editor to skip the 2% of the game that isn't fun." The Binding Of Isaac Repentance Save Editor
The Accessibility Argument (The most important): "I have a motor disability that prevents me from dodging fast projectiles. I will never beat 'The Beast' as Tainted Lost legitimately. A save editor is the only way I can see the ending cutscene or use the 'Death Certificate' item."
The Verdict: It is a single-player game. Using a save editor harms nobody. However, you should not upload edited save files to speedrun leaderboards or claim legitimacy in competitive mods. Furthermore, using an editor to unlock everything at minute one often backfires—players report losing motivation instantly because there is no goal left. The Isaac community is surprisingly divided on this
The Binding of Isaac community is weirdly split on save editing versus modding.
The Purist Argument: "The difficulty and grind are the point. Getting Dead God is a rite of passage. If you edit, you didn't earn it." The Binding of Isaac community is weirdly split
The Pragmatist Argument: "It's a single-player (mostly) game. Your save file does not affect my enjoyment. Gatekeeping item unlocks is weird."
The Verdict: If you are going to stream speedruns or submit to leaderboards, obviously do not edit. If you are a Dad with two jobs and 45 minutes a week to play, and you just want to experience the Fallen Angel transformation, use the editor without guilt.
Even with a perfect save editor, Repentance fights back. Here is how to avoid ruining your game.