The idea is that a more advanced 3D printer would be able to deal with issues like that.
Except... it can't. Its physics, you can't get around it. While power metallurgy can create strong metallic pieces, using 3d controlled laser sinterers, They simply cannot create pieces with the properties that are required to make many things in the world that we use and rely on today (particularly because of the fact that you have gaps in your metal).
Main example: Roller and ball bearings. To get the required hardness you need to forge the material that the race is made of (IIRC), and then apply heat or chemical treatments to it to greatly increase the surface hardness. IIRC, they usually heat treat them to turn the steel into martensite, which involves heating the metal upto 800C and quenching it. After which the races need to be machined for precision.
So... a more advanced 3d printer would be capable of say, making a bearing, would probably require the facilities to forge a race, something to heat the metal upto 800C, and the ability to precisely machine, not to mention the specialized equipment to correctly make the perfect sized round balls. I think that any 3d printer/automatic assembly machine advanced enough to do that would look exactly like bearing factories
that already exist today. Not something that the average person would have in their back shed...
edit:
Some of this stuff is realistic, but 3D printing is one of those things people sometimes extrapolate far too much upon.
That's pretty much what i'm getting at, i guess.
I think one thing people have to realize is that its already quite possible to make stuff on your own, you don't need a 3D printer to do it. Go buy some sheet metal, a welder, and maybe a heat torch and tools, and you can cut, bend, weld and create a great amount of things. A lot of the fabrication in the world is done by small local shops who make custom things (particularly in the auto industry, for example. Hot rod makers, engine builders, etc do this all the time, eg making custom mounts for things). but that hasn't caused the entire economic model to collapse. I don't think more advanced 3d printers would either.