Out of this world Keynesian

Last Sunday, I worried over negative-NPV stimulus.  No problem.  Paul Krugman believes that even a false-alarm invasion of the space aliens would get us to spend our way out of our current economic situation -- as did World War II.   I had thought that Bob Higgs had successfully debunked the latter.  I would love to see Higgs' arguments taken on by Krugman and anyone with similar views.