This is a great example of the space fallacy, the idea that things that are impossible to do on Earth are somehow practical technologies for space. If it's all so easy to do, then go hollow out your local mountain; I promise it will get people's attention.
I'd settle for hollowing out an actual rubble pile as a demo. I'd be ecstatic, honestly, if you dumped any package of machines on a rubble pile and it autonomously, with only solar power, produced any machine more complicated than a bar of metal (and even that bar of metal would be no joke). Refining raw materials is hard. At least in space you'd be able to melt things in the open without them immediately oxidizing to hell.
Gravity is dubious as pro or con. It's honestly kind of handy sometimes, as a spatial organizing principle if nothing else.
