I believe hackers in general are a legitimate concern.
This year it’s terrorists. Before that it was hippies. Before that pinkos, and just before that, reds. The wobblies came before the reds, and before that it was the damn Sun Dancers, who displaced the copperheads. Only reason to be concerned about copperheads is that witches weren’t around any longer, but before witches was the heretics. Before heretics were a thing, it was roundheads and cavaliers, although it’s hard to say which came first, they switched back and forth so often. And before them we had heretics again, except they were new enough at the time to be called protestants. Or was it philistines? No matter, they had their time in the sun too, so to speak.
Yeah, let’s all cower under our beds in fear that robots, which don’t exist yet, that are built by scrap iron eating printers, which don’t exist yet, will be hacked by terrorists. Is this something about hacking them over there so we don’t have to hack them over here? Problem with printing machines is that machinery is made of materials with different properties. So if you want to build something more useful than an action figure or a fancy paperweight for your paperless office, you’re going to run into parts that are too soft, too hard, too brittle, too flexible or otherwise unsuitable to be used with the parts that your particular resin does get right. So instead of using your desktop printer to manufacture that cool set of headphones or a spare ballpoint pen, you’re back to the store again to just buy it.
Life goes on.
I think in 20 years you will be able to print a whole working smart phone,
however I think people will be printing swap-able components like project ARA pieces,
however the pieces will be quite small, and usable in any device print, like camera sections, or LED 1cm x LED 1cm
so the same tech to print a phone will print all the pieces a assembler arm makes a TV from,
some parts will be of a more Macro scale, like strong actuators etc,
Printablility + molecularity together will eliminate a lot of waste.
in the meantime, you can use a arc furnace to melt metal, (made from 2 microwaves) and then pour into a 3d printed cast…
then clean it up and build anything.
plastic, metal, ceramic?
there is no limit.
Also laser sintering of exotic materials as well as composites will also enable some very tough things to be made.
I think the household printer of the future will contain a sputtering chamber, as well as potentially a lithography system.
Somehow, I don’t think it will be worse than people printing on expensive paper using expensive ink. There is always going to be the person that prints more than he needs and wastes ink and paper and contribute to the paper crisis(!), but realistically the materials will most likely be expensive and the last thing people will want to do (after the novelty has worn off at least) is waste it.
@BPR: don’t want to harsh your mellow, but have you ever melted metal and poured it into a cast, then cleaned it up? I have. It’s definately a ‘kids: don’t try this at home’ kind of operation. And there are limits… what if that part needs machining, or needs to be put in a drop forge and hammered, or tempered? Die hard do-it-yourselfers already have mini machine shops in their garages, and might have a casting pit in the back yard, next to the kiln and the compost heap. But I think your projections that this will become a common part of a home economy are a mite optimistic. 
I think that automation and tool heads can do many things.
and one day your 3d printing machine may be a Robot with a printing arm,
or forging skills or?
A robot will soon be able to do alot…
Midget robot blacksmith Go!
also, I made thermite once… for… science
I have not cast anything, but lived near a large foundry and my step dad was a machinist.
I understand that heat treated steel can be springy or brittle and hold a edge or?
I know about forging and drop forging etc.
Just a week or so later, we now have a competing product from Australia that does the same technique, but with a different approach.
It will be pretty pricey providing that the Kickstarter campaign succeeds, but it seems like there’s genuine interest in the idea as a faster way to create objects.
[video]https:/youtube.com/watch?v=s9t2ZNn43LI&feature=youtu.be[/video]
damn nice print as well,
I wonder how tough it is?