Fun because you like rewriting existing code?

Rust4Linux is not a “rewriting” endeavor.

Fun because you already have test suites you don’t have to rewrite?

See previous point.

Fun because you feel morally superior by writing fresh code, even though the old code is running critical applications in production?

Can you point to where “moral superiority” was used as a reason for using Rust in the Linux kernel?

Can you point to an example where Rust code in the kernel caused breakage in “critical applications in production”?

Bonus: Do you think “critical applications” closely follow mainline?

Fun because you think your smarter than the engineers that lay the ground work before you?

Who were the engineers that came before Greg Kroah-Hartman?

What ground work exactly are you referring to?

How does Rust code in the kernel relates to this?

Fun because you like hunting bugs you created thinking you know better, while calling your rewrite superior.

Better than whom?

What rewrite?

Where was it stated that the fun was in hunting more bugs?

Bonus: Do I actually prefer it if someone other than the original coder is hunting bugs?

And to finish with a meta question:
Why the likes of you feel the need to share opinions based on fictional events regarding matters your clearly completely clueless about?