"Why do we need a space station on the moon"
Same reason we need one in orbit in space. Refuel/resupply for shuttles- plus the moon has 1/6th(is that right?) gravity than earth... that's a LOTTA rocket fuel you won't burn up trying to simply get into space.
Basically a moon station, or large enough space station, would make space travel feasible. Only problem is that it would have to be self sufficient for long periods of time without resupply- especially on the moon.
The first step would be space station (permanent one, easily repairable, easily resuppliable, large enough to act as a space harbor for shuttles), then build a moon base (orbit will never decay, it will have access to it's own minerals, possibly water too, and have to be able to make it's own oxygen and have a fairly large colony to operate it)...
So basically, if you wanna go any further out than the moon with manned missions... then we NEED a moon base.
-SW