And make the parts out of what? Unless you set up mining and manufacturing facilities on the moon, at which point you could set up traditional manufacturing facilities for anything and 3D printing isn't necessary, the raw materials would still come from earth, as would the water, food, and fuel.
That is where colonizing comes in.
3D printing out of all kinds of substrates is getting to be common. I'm sure there is a way that basic polymers can be used at first.
Hell, make it out of moon dust!
The upfront work will be huge. HUUUUGE I tell ya!!
The idea would be to set up a small colony/workshop on the moon (think the Antartica science "community"). Once that is up and running, begin planning/working on project to go our further to explore.
I know I glazed over the years and years and years and years and YEARS of transporting, building, acclimating, farming, and basic living. But that is what it is going to take. It is also going to take a multi-national effort. This isn't a US thing. It is a human being thing.
And of course, this is all pie-in-the-sky talk from me. I'm just a guy in the midwest with an associates degree from a community college and a desk job.