> The Linux kernel—one of the most well-tested pieces of software today,

I feel like these people aren't really experts in the field of testing... Linux is not known for its testing... there's plenty of good things one can say about Linux, but great testing isn't one of those.

Now, things that are well-tested are things that do critical stuff, like avionics, power-plant control, medical equipment, storage... It's software from a different league.

Linux is too big, too dynamic, too distributed between different authors to hope for great testing. And it's OK. I'd rather have more people being able to contribute, not being constrained by the difficulties of the testing than have a very well-tested and borderline useless system.