This quote is one of the most poignant parts of this letter, because it highlights the optimism of those pioneering space and the ultimate failure of their (lofty, laudable) vision.
War is not only a catalyst for technological advancement, but acts as economic stimulus, spurring industrial development and job creation - the business war is, sadly, one of the central pillars of the largest western economies (including the UK).
Could space exploration, which has similar properties, ever fill this role? Is there the political will to dial down the military-industrial complex and replace it with a "space-industrial complex"? Will extraterrestrial concerns ever factor as highly for governments as parochial ones, and will space programs ever see parity in funding to military endeavours?
As a stimulant and catalyst for the development of new technologies, and for research in the basic sciences, it is unparalleled by any other activity. In this respect, we may even say that the space program is taking over a function which for three or four thousand years has been the sad prerogative of wars.