Well run the math. Which would take more energy to loft: An thousand ton ice cracking plant out of 1G gravity well, dropping it on the moon and letting it process for a while autonomously before then lifting a million tons of cryogenic oxygen and hydrogen out of .17G gravity well, or lifting that million tons straight out of the 1G gravity well to start with? It is an economy of scale. The amount of consumables you need to lift out of earth's gravity well to reach the moon is trivial compared to the amount required to reach any other celestial body. Note this is for manned flight. When you look at the amount you would need to reach Mars or the Asteroid belt what you would save from having a reduced gravity well is immense. Plus here's another point. The moon doesn't have an atmosphere. If you had fuel lifters at the moon running round trips from surface to orbit they don't have to worry about reentry shielding, and as the lunar landers from the Apollo program show, single stage to land, single stage to orbit at the moon is more than within our ability. We have yet to create any single stage to orbit craft that can loft a decent cargo here on earth. The resources that we throw away each time we lift something to low earth orbit is astounding.
Now, once you have a suitable generation plant running on the moon it can use an automated reusable lifter to loft the readied fuel into lunar orbit and then return to the plant for more cargo and to refuel itself (since that's what the plant is making). Short of maintenance issues this can continue indefinitely. With this in place the only things you really have to worry about lifting out of Earth's gravity well are the materials for construction of said interplanetary craft. Once it's assembled it's just a quick jaunt over to lunar orbit to pick up the stockpiled fuel and then head out to mars/A.belt. If you also found a suitable large icy asteroid and sent a similar automated fuel plant to it, as you did the moon, you now have a refueling point for the return trip, halving the consumables you would need to take with you. Or, you could start doing hops, moon->asteroid->Europa/Ganymede.