I wonder if sometime in the future, we will have exhausted Earth's fuel and metal resources so badly that we are no longer capable of building the tools necessary to make our way into space, including projects like this one.
Metal resources don't get exhausted -- nearly all of the copper mined at the time of the pharaohs is still in use. When the cost of mined material rises, we simply reuse some of the metal that is in use in lower-value places. Example: all the copper piping that is presently being ripped up and replaced with plastic everywhere in the world.
Nuclear fuel resources are essentially inexhaustible -- there is enough Thorium to feed constant growth for at least tens of thousands of years. Which should be enough for development of fusion.
According to the International Copper Association, more than 80% of all copper ever mined is still in active use. Copper doesn't materially degrade in use -- used material can simply be recast or rewrought for a new use.
