Peter A. Taylor (who seems to have occasionally read some LW/OB) has a few interesting essays on that on his home page:

• Why are space launch costs so high?

• Conflicting Visions of the Manned Space Program

• Where (in space) do we go from here? or Why do we have a manned space program?

I don't remember all the content of those essays, but the gist of what I remember is that we don't have a clear idea of why we want to go into space, and some of the goals (such as preparing space colonization) would be better served through other means (such as getting better at making self-sustained hermetic ecological systems, which can be done in a basement).

On an unrelated note, fans of space conquest might enjoy the song Fire in the Sky.