Why should Perl special variables get a pass on that?

If you, as a "former monk" don't understand, then it both explains why you left; and why nothing I could possibly say would make the slightest bit of difference to your perception of this situation.

The key indicator here is your phrase: "Mutating global state is bad."

By which you mean: varying variables with top level scope. is verboten; (by you!)

1. There is no point in having variables; if you cannot vary them!

   Variables that do not; or are not "permitted" to, vary, are constants.

   (It is this, beyond the performance penalties, that make Readonly a nonsense.)

2. Every program has a 'top level scope'.

   Choosing to differentiate between "global variables" and "top level, lexical variables" is a sham. A pointless and puerile non-distinction.

   Further, every (useful) program ever written makes some assumptions about ... whatever. This is usually referred to as "configuration".

   So your (bland and uninteresting; unless you bother to follow up with some supporting argument) statement reduces to: is there any legitimate reason for a program to ever override its startup assumptions?

   And fine, if you can sit wherever you are, and hand-on-heart, conclude that there is never a legitimate reason for a program to override its startup assumptions; then you've won the argument.

   But, before you pat yourself on the back consider each of these:

   • Have you never written a program that needed to override the default assumption about what constitutes a newline?

     Eg. A *nix program that used sockets.

   • Have you never written a program that needed (or benefited from) overriding the default value of cwd?

   • Have you never written a program that benefited from overriding the default setting of STDIN, STDOUT or STDERR?

     You've never used the one-arg form of select; nor redirected STDERR to a log file?

   • You've never messed with %INC?

     Eg, used lib?

   • You've never tweaked %ENV?
   • How about installed your own signal handler in %SIG?
   • You've never felt the need to reset $@, $!, $^E, and $? before running code that might influence them; and which you need to make decisions upon the values they might acquire?

If you can say "No" to all of those; then you've both won the argument, and are either a liar; or not a programmer.

Being selective about what functionality you accept as legitimate, and what you personally choose to reject is one thing; attempting to impose your affectations upon the world at large is another.

Why bother saying any of that non-message related stuff if your message is what you want people to focus on?

My argument isn't strong enough, so I'll distract with the sentimental nostalgia

Mutating global state is bad. We all know this. Why should Perl special variables get a pass on that?

Hehe, why single out special variables, like STDIN/STDOUT/STDERR/@ARGV, why not single out perl itself? I mean global namespaces and all that, that's ten times worse than the special variables