That's right.  If you desperately needed that functionality, you could patch if.pm as shown below. (In case you'd rather not mess with the system version, just create a copy in some local lib directory and make that directory be searched before the system ones.)

You could then for example write

use if $DEBUG, 'Data::Dumper' => undef;
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to import nothing, just like with

use Data::Dumper ();
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As the module is actually rather short, here is the full code:

package if;

sub work {
  my $method = shift() ? 'import' : 'unimport';
  die "Too few arguments to `use if' (some code returning an empty lis
+t in list context?)"
    unless @_ >= 2;
  return unless shift;        # CONDITION

  my $p = $_[0];        # PACKAGE
  (my $file = "$p.pm") =~ s!::!/!g;
  require $file;        # Works even if $_[0] is a keyword (like open)

  return if @_==2 && !defined $_[1];    # <--- ADDED

  my $m = $p->can($method);
  goto &$m if $m;
}

sub import   { shift; unshift @_, 1; goto &work }
sub unimport { shift; unshift @_, 0; goto &work }

1;
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When being passed undef, the line marked with "<--- ADDED" would make the sub return before executing the real import() of the target module via goto &$m (where $m is referring to import in this case).

(Not well tested! &mdash use at your own risk...)