Is it safe to quit kernel_task?
Killing kernel_task is "killing" your entire system.  

It's not the same as logging out; it's asking you to log out because everything will be going down.

From What Is kernel_task, and Why Is It Running on My Mac?


  A “kernel,” if you didn’t know, is at the core of any operating
  system, sitting between your CPU, memory, and other hardware and the
  software that you run. When your turn on your Mac, the kernel is the
  first thing that starts, and basically everything you do on your
  computer flows through the kernel at some point. Activity Monitor puts
  all of this varied activity under one banner: kernel_task.