While most don't understand it yet, the driver for manned space flight is going to be dealing with the impact hazard, specifically the comet impact hazard.

Dark carbonaceous chondrites, which appear to comprise about 50% of the "small" impact threat,
are simply too dark to be detected with any passive optical system. Perhaps IR systems can be improved to the point where they can be used, but I doubt it. These are 100 meter objects a far distance out. If you "need" active detection sytems, and I am convinced that "we" do, then they will have to be built on the Moon.

The other part of the impact threat is long period comets, and again, Moon based observatories offer about 6 months more warning. Given the masses involved, and the simple physics of changing the path of those masses, those 6 months are critical. For comets, there certainly will not be 20 years of warning time.

What happens after the Moon based detection facilites are built depends on a lot of questions, most not answered, many not even asked yet. Will He3 be necessary or useful for fusion power generation? Can Mars be put to any useful purpose? Will a change in transportation costs make the use of space resources profitable? Will SETI lead to results?

Have a nice day