in reply to Re^2: Scurbbing a string
in thread Scrubbing a string

I would have thought the same. But you could get around it by building your RE as a string and then putting that into the s///:
my $allowed = "pure"; my $re = "[^\Q$allowed\E]"; my $str = "p uuu+tr-ed"; $str =~ s/$re//g; print $str, "\n";

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