If your users are not engaging with your app, you can't deliver user value to them. If you are unable to provide value to their lives because they happened to accidently changed a font that is an unfortunate circumstance where the user is losing out on value they could have had.
It's not that users are helpless, but that they just don't want to spend their time dealing with stuff they don't want to. Users like it when things "just work."
Users who want things to "just work" aren't the entire target audience of software, and it's a huge misstep to act as if they are.
There is nothing wrong with providing sensible defaults and a good collection of pre-designed profiles to choose from (and yes, even a big, friendly RESET button).
But that doesn't explain taking away options. Users who don't want their time with this stuff would probably not use the customization options in the first place.
Also, the term "deliver value" has been badly tainted after too many companies have used it as an euphemism for "extracting value".
It's the same non-logic that advertisers use: Ads are both a service for the viewer, informing them of amazing opportunities, but also somehow the viewers must be forced into consuming that service.
I'm deeply skeptical of situations where people have to be forced into something "for their own good".