you seem to be mixing "errors" and "warnings"

Yes, I've mentioned that a couple of times during the design meetings, but I think we came to a reasonable understanding: there are "failures" (die/croak), there are "non-fatal errors" (error), and there are "warnings" (warn/carp).

Examples:

• failure: unable to connect to a required database. The software can't proceed, so it croaks an exception.
• non-fatal error: user input failed to validate. For example:

  if ( $obj->validate($q->param('new_userid')) ) {
     create_new_user( $q->param('new_userid'))
  }
  else {
     # tell the user why it was invalid and ask again
     send_reprompt(
       "UserID was not valid for the following reasons:"
       $obj->error
     );
  }
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• warning: couldn't connect to the primary database, had to fall back to the secondary.

Things like the second case often generate several errors simultaneously, since (for example) a userID can be invalid in several ways -- a situation that the die class of functions doesn't handle elegantly. That's the purpose of the error list in this core module.

Additionally, it provides a compromise to things like:

eval { $obj->get_stuff_a() }; if ($@) { $obj->try_a_backup() }
eval { $obj->get_stuff_b() }; if ($@) { $obj->try_b_backup() }
eval { $obj->get_stuff_c() }; if ($@) { $obj->try_c_backup() }
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Allowing, instead:

$obj->get_stuff_a() || $obj->try_a_backup || die $obj->error;
$obj->get_stuff_b() || $obj->try_b_backup || die $obj->error;
$obj->get_stuff_c() || $obj->try_c_backup || die $obj->error;
my @err = $obj->error;
if (@err) {
   warn 'Had to use one or more backup sources because:'."\t\n"
       .join("\t\n", @err)."\n";
}
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The latter is more useful for logging (and, IMO, more understandable when read).

Often, our developers will approach cases like this by simply dying on the first error they encounter. While that's "correct" behavior, it frustrates users and other developers when they have to try an action repeatedly instead of finding out everything that's wrong in one swell foop {sic}.

Given that further information, would you still advise me to croak instead of carp on DESTROY?