Why is immutable a requirement?

Who said anything about critical?

I just don’t want my hard disk wiped when I decide to try a piece of software.

Security updates if you use it online or copy new binaries to run on it. Even if you’re not worried about hackers, there can still be viruses and malware that destroy your data.

Lots of retro enthusiasts still use legacy hardware for all sorts of reasons… I fear that a fork of the kernel will be necessary in the near future to keep these machines running.

The notion of using Linux to revive old hardware and keep it out of the landfill may not last forever…