Short answer - piss flows downwards in the gravity well. Longer answer: 1. Water - we need a lot of it for everything. There is not much on the moon. There ar

Short answer - piss flows downwards in the gravity well. Longer answer: 1. Water - we need a lot of it for everything. There is not much on the moon. There are few ways to do it - there is a lot of oxygen on the moon so we only need the hydrogen. Lifting from the earth will be hard, capturing protons from the sun wind seems feasible - but is unsolved. 2. We lack in robotics and nanotech. A perfect colonization plan (also cheap) will require us to lift only the wetware. (even better pre frozen embryos) So if we manage to create self replicating GECK (solar cells, 3d printers, etc) that weights about 2 tonnes. Deploy it there, wait for it to devour the moon (since its exponential it could be just a few years), gather enough water and then send small teams 10-20 fertile women with a lot of embryos to be serially mothers for rent ... we could see something in our life time. Since the moon will be one giant solar cell you could beam the excess energy to the Earth and the moon is much better base to try to tame venus mars and the belt.