Origin of life: There must be life out there! vs. There can't be life out there!

Robert Deyes provides a helpful summary of the see-saw between the belief that life must exist on other planets (inevitablists) and that it cannot (impossiblists):

'Life, Life Everywhere' was the title of a 1996 article in Scientific American that focused on the crucial question of whether the origins of life were truly an inevitable consequence of some fundamental natural tendency in the universe towards great complexity (Ref 2). From our modern stand point, it was really Fred Hoyle that challenged this 'inevitablist' school by proclaiming vehemently that, "the emergence of a living cell from an inanimate chemical soup is about as likely as the assembly of a 747 by a whirlwind passing through a junkyard" (Ref 2). So the modern 'improbabilist' was born, taking on the contrasting inevitabilist view in a head to head intellectual battle. While the inevitabilists used the sudden appearance of the cell almost 3.85 billion years ago (Ref 3) as evidence of life's inevitability, improbabilists such as the late Francis Crick proposed that life was unlikely to have arisen on earth and must have been seeded from outer space (Ref 2). After all if life were truly a rare phenomenon, space transportation networks would have been required to spread it around hospitable planets.

Hmmm. The middle ground between inevitable and impossible is about as solid as the middle of a Lifesaver.