There are things in which we are pretty sure. What evidence is provided by an unsupported suggestion that a particular doomsday scenario is possible? We can't bother to investigate every crazy doomsday scenario suggested, so something must establish the priorities. How much value does investigation triggered by an unsupported a-priory crazy idea about a particular form of existential risk, add to general investigation that is interested in considering any possible scenario? High public interest might warrant a public relations action, but why should it in itself require serious study?