Yes, actually harmful.
The file utility can be useful. Don’t know what program to open a file with? Run file and it will tell you. Of course, sometimes file will be wrong and misidentify the file type. This may be inconvenient, but at least as a user you still have the option of trying to run another program.
Except when you don’t. What happens when file (or its programmatic buddy, libmagic) is not a hint, but a gatekeeper? What happens when some application determines its behavior based on the output of file?
What happens is you can’t print on Tuesday.
Or you can’t print particular documents that contain inappropriate phrases.
Or you can’t launch a browser and consequently prevent Firefox from providing ASLR enabled builds.
A program that helps users is useful. A program that restricts users is harmful. Run file on your computer all you want, but don’t use file to limit what I can do.