Before we begin to imagine the benefits, and before we can publicly discuss what life would be like if every home had the ability to 3D print an unlimited number of useful things, it seems that first we must have a never-ending gun debate.

The reason that 3D printing is being coupled with easy access to guns may go well beyond the 'gun debate' itself.
This 'guilt by association' is probably more like a propaganda device, and is being sustained by those who would lose the most in the new socio-economic paradigm that 3D printing technology is bound to help to create at some point in the near future.
3D Printing Being Painted as the Villain
With plastic straws now banned in California, it's easy to see how simple objects can become the victim of mass confusion in a group's mind. The group mind is never logical, but is easy to mould and manipulate, and the professional social engineers who manage the culture that we live in-- certainly here in the USA-- have been directing this group mind for decades.

First, they came for the drinking straws...
Let's look at the drinking straw ban. Who will be the first to be imprisoned for putting the blueprints for 3D printed straws up on the internet, for all to see? What frightful things will people be 3D printing next? Can we ban all printable objects, or should we ban the 3D printer itself? Let's ask the group!
Examining the Group Mind
Given the information that is made available to the group, the consensus of the masses is going to be based on fear, as usual, and that fear will guide the group mind into a general need to be protected from evil. The drinking straw, suddenly a thing that is now synonymous with evil, must be kept out of the hands of bad people, and any technology which allows the manufacture of such evil items must be stopped at all cost.
Now, according to the group's mind, there seem to be people who can 3D print straws and handguns freely, and the obvious solution to that perceived problem would be to halt the 3D technology, by law and at gunpoint if needed.
3D Printing; A Threat to National Security?
The real reason to demonize the 3D printer in this way might be more of an economic issue. The 3D printing industry would be bad for scores of established industries in the USA and around the world.
Transportation and trucking firms would suffer when a lot of the stuff that they used to truck around the planet could be manufactured at home on 3D replicators.
As 3D technology advances, the cost of many common items would decrease, and sales taxes would suffer.
The timber industry would fall without a sound when home builders began replicating lumber right on the job site, instead of using pine trees and real hardwoods.
Each technological advancement in the newest replicating devices would cripple another established industry, and the lobbyists for those industries would have no choice but to push for regulations and bans on 3D printing.
Those who stir the debate about 3D printed guns may not be so concerned about the public's safety as they are concerned with their businesses and their bottom lines.
If the masses are not dependent upon the trucking industry bringing lumber from the timber industry using fuel from the petroleum industry to build the houses and offices and restaurants, and to then fill those buildings with all of the things that were formerly made overseas in giant trade agreements based on shipping costs and time, then those masses of people who live in the world would be richer for it, and would then begin to see a better way of doing a lot of other things for themselves and their society.
Decentralization
The potential for the technology of what we call 3D printing amounts to decentralization, something that is familiar to those who study nature, cryptocurrencies, blockchains and fractals.
As the technology improves all the time, what would the world be like if everyone had a 3D replicator in their homes, or at work?
Out of necessity, various bio-plastics would be developed, so that local sources of the printing medium could be used to manufacture larger pieces, and things like hemp would come to mind for those who dared to imagine localized, sustainable systems of life.
With a few sacks of seeds and a portable replicator, one could homestead like never before, growing the materials for their house right on the spot, then piping it into the replicator to create flooring, insulation, joists and girders galore.

The Benefits of Decentralized Replication of Goods
If 3D printers are somehow allowed to remain legal and unregulated, then new industries would be created in the wake of the technology. A technician might need to show up in his 3D printed service van, land on the lawn and repair a replicating machine on occasion.
If we can freely explore the potential for the decentralization of production, then we would find that a neighbor who is good at growing hemp would trade freely with another who knew how to refine it into oil, while builders would show up to construct solid dwellings using the materials that were produced right there, made from the very Earth below.
The control of the society's resources would fall into the hands of the individuals who were living in it, and there would be no need for high prices of things if those things were being grown in the back yard by the individuals themselves.
Enter, The Group Mind Again
It seems inevitable that the collective mind will see danger in the idea of unregulated 3D printing, and will point to the straws that still litter the world, or simply cry out the old trigger word, the tried and true four-letter word; GUNS.
So triggered, the collective mind will gasp that the only way anyone will be able to operate a 3D printer will be if they obtain a special license and permit to think about using the technology for anything but paperweights and bathtub toys. Citizens will be encouraged to report anyone who tinkers with printing, and of course all subversive 3D printing videos will be scrubbed from the internet.

Guns are Scary
For the social engineers who run the group's mind every day, there are no bigger problems than the problems of a decentralized system of distribution, and the idea of a financially freed society, a society with time to think about things.
While the gun is a handy tool to control the masses, it is always the mind of the society that is the true danger for those who manage our culture today. The fear of guns can be used to trigger emotions, but that trigger is used so that the group remains dependent on the central control that has been maintained for so long, masquerading as the security force for the population.
We are now expected to think of guns when we hear of new 3D technologies, or we won't hear about the new tech at all. We are expected to fear for the children, instead of imagining the beauty of living in a financially freed society for once.
It looks like the war on 3D printing has officially begun.
