I ran "poweroff" as a regular user -- and the system shut down.

  The  reason  is  polkit. By default, on a freshly installed system, it
  allows any user to initiate a system shutdown.  Maybe  more,  I  don't
  know and I haven't checked.

  The  end is near. I no longer feel like I'm in control of this system.
  It no longer feels like the system does nothing by default, unless you
  tell it otherwise.

  The  same goes for this new trend of auto-activating daemons. What the
  shit? If I want a daemon running, I enable it.

  I now maintain a list of stuff to disable on my systems:

  gopher://uninformativ.de/0/txt/gnu-linux-notes/arch-disable-annoying-daemons.md

  Funny enough, everything I do  still  works  after  disabling  polkit,
  rtkit,  colord  and  avahi.  There  is  no  fundamental need for these
  daemons, they just might be useful in some situations for some people.

  This is a disaster. Stuff like that is the reason why I  left  Windows
  many  years ago. It's the reason why I chose Arch Linux, which used to
  do nothing unless you told it to.

  So annoying. Linux, the kernel, has many  useful  features  and  great
  hardware support. I don't want to miss that by switching to one of the
  BSDs. But with all that freedesktop.org fuckery going on, it's getting
  harder every day to maintain a more or less non-sucking system ...


                           ____________________


  Just  to  clarify: Simply disabling these daemons is not the solution.
  It's a hack and it's prone to cause problems.