Utter Hogwash !
Having done a bit of Rapid Prototyping in my time, I have to say this piece is garbage on many counts.
Owning a 3D printer doesn't make you a manufacturer any more than owning a paintbrush makes you Van Gogh.
Owning a Lexmark now doesn't make you Harper Collins!
The CAD files that are used to create things are never released to the public. There are 3D laser scanners in existence but they can't reverse engineer!
How many people could turn a kit of parts into a new Robosapien, car or TV?
You can buy home CNC lathes and milling machines but Ford is still in business isn't it?
>>>>"3D model complete with cavities, but without overhangs (as these would have to be suspended in the air while the connections were laid down)"<<<<
NO! 3D printers can extrude at least 2 materials already. One, the build material and one for the support matrix. So something like an open umbrella can be grown self-supporting. The support matrix is soluble and washes off leaving the finished part.
It will be a good hundred years before these machines can make other machines or replicate themselves. Making a cosmetic shell is one thing. Making high value structural parts is currently inconceivable.
You want a Daily Rail red-top scare story? People could "print" knives and guns AGGGHHHHHHH !!!
BAN THEM, think of the children etc. etc. etc.
Don't extrapolate a Bit Torrent into the real world.