>That's like going back to the 17th century and decrying the exploration of the New World because you're not certain just how much gold there may be and you can't predict what the New World economy might look like.

No it isn't. Exploration of the new world offered obvious substantive benefits - the trees alone were priceless to a countries that had to manage forests very carefully, not to mention new and useful crops coupled with an abundance of land. In short, it was a no-brainer.

And it was extremely cheap compared to building space infrastructure, since food could be grown or purchased from the natives, there was air, sunburn was the only radiation problem.

In space we'll have none of that. There are unsettled regions on earth far more hospitable to human life than anything we'll find outside our gravity well. The idea we ought to sink trillions of dollars into and infrastructure to produce things that are already good enough is hard to justify.