Considering what it takes to build a 3d printer, they would have to "control" way to many common electronic and mechanical parts. A Raspberry PI open source embeddable computer, some stepper motors, software you can download from the internet and some basic wood fabrication skills, and you can begin to print. Maybe even print a more refined cabinet for the next printer. Of course this method will take hunderes of hours of labor and tinkering before you can print that lovely purple Yoda head you've wanted.
Also the printing of guns is a bit of a concern especially if they are able to print it with an entirely non-metallic medium (like ceramic). But there are still thousands of machinists who could produce a metallic gun today with basic metalworking tools -- how many years have we had lathes.
I think the 3D printing technology is is only the beginning. At some point they will develop a completely automated "pick and place" machine that will print it's own boards and all you have to do is feed it with raw materials for the boards and electronic components. If you combine these technologies along with nearly universal CNC metal machining (just about every metalshop that's busy has one of these), there's literally nothing you couldn't build.
"Star Trek Replicators" here we come.... lol