I appreciate your concern, Dudley, for the way we have been changing the biosphere of Earth in the past and current century, and how dangerous that may be for the survival of our civilisation. But Bostrom’s speculation regarding Fermi is not about one possible end to our civilisation. The postulated black ball is something that will end any civilisation, wherever it may arise and whatever form it may take. In fact, it would be something that always occurs and inexorably leads to destruction, and always, without exception, occurs before the advent of interstellar travel. Otherwise we would find evidence of alien life in our system.