I’m thinking of adding a “creative mode” to my game. But also kind of think that this might spoil the game as it would disinsentive people to play through the game if they can just go on creative mode with infinite lives and infinite resources.
Then again, I’m also thinking that why should I make people play through the entire game if they don’t want to?
It’s a dilemma.
What do you think?
You did not say what type of game you’re making.
For many types of building games, the creative mode is a big draw to some players, and sometimes the only draw. Even in a game like Stardew Valley, people create mods to allow the use of decorations and other changes because they want to focus on free building while still playing through.
If you have a story game, there are people who will just want to see the story. Some people like playing a game on “easy” combat or where the puzzles can be skipped so that they can get to see the game without being gated by things they find frustrating to get past.
Of course, depending on your genre, folks on the internet will cry “cheating” and other such silliness, but then there are folks on the internet who think anyone who plays any game at a less hardcore setting is a lesser person, so ignore the internet. 
Yes, good points. I think I better make sure there’s things that you only get to see when playing the game, such as cut scenes or special ending animations etc.
There’s lots of different ways of going about this really. Take the various Parodox games, where you can create mods, go back to old saves, etc, but playing in that game mode you cannot get any Steam achievements. You’re required to play in “Ironman” mode to get achievements which restricts your game options and overwrites old saves with new ones automatically. It seems to be a good balance between the two.
Games like Minecraft have their creative mode which just lets the player have fun with the thing without any challenge. My son with his cousins like to play in that mode together because they are just laughing nonstop at all the silly things they are doing. No challenge, but they are really just trying to show off their creativity rather than skill to each other.
No more than adding a metagame ruins a game.
I have no issues with Creative or Cinema (super-easy) modes, even if I never touch them myself. Even if you can get all the items, trophies or cutscenes. So what if other people can get those without stepping up to some challenge? In my experience most people won’t have issues with that, as long as the game is not competative.
And thus SP games like Skyrim / Fallout disable trophies when using mods, since they invite comparison with other people’s trophies: you could explain that as a competative element. Avoid those elements and few people should have issues with a Creative mode.