I think it's perfectly OK to exploit the moon. Largely for two reasons: there's no life there, and it is close enough and rich enough in resources to be economically useful to Earth. In the final analysis, everything we do in space, if it does not help the people of Earth, all the people, it's not going to happen.
As quoted in "Men on Mars, Women on Venus" by Jay McDonald at Bookpage (June 1999)