Opinion - Why Space?

Since, as I said in my last post, I'm not pressed for time, I thought I'd do a quick opinion piece. Lately, with the presidential primaries in the US, there has been some talk about the reasons for having manned space exploration funded by the government. Personally I can think of only one really important reason - to set up the conditions for economic growth to continue into the long term future. The expression 'environmental sustainability' has reached popular recognition and acceptance, and for good reason. However sustainability has its own risks if carried into the long term. Stagnation, both economic and social, are the inevitable result. A much better model is gradual economic expansion, which can really only be supported by harvesting space based resources.
Until recently, I thought this would be a good argument to use to convince government that it is worthwhile supporting research into technology leading to space settlement, but apparently, some don't believe in such long term planning. Funding of the ITER project by the US government has been slashed to only $10.7 million this year, from $160 million promised. The reason given from the article: “R&D resources just aren’t there to support projects that are so expensive and have shown so little potential for promise in the near term.”
If that attitude is carried over into space exploration, then the inevitable conclusion will be reached that there is no compelling reason to fund crewed space exploration at all.