Distributed manufacturing can't compete with the economies of scale from traditional manufacturing where a highly expensive, specialized single purpose tool is used to fabricate a gazillion high quality widgets at cheaper per unit cost, than the plastic piece of crap that you could get from a 3d printer. But for certain one off specialty items, yes a 3d printer is supremely useful and economical today.
That's entirely true for the current generations of 3D printer, but how do you know they won't improve in the future? If printed tools ever become good enough or almost good enough to compete with the quality that a traditional manufacturer can provide, they definitely have a chance of becoming more economical. Cutting out transport, work, and other such costs can make up for it.
I don't know when that tipping point will happen, but it would surprise me if it's decades for common tools. Printers have made great strides in just the last few years, and if the current pace of development keeps up, they could reach parity in the very near future.
I'm not sure this is true. "Plastic piece of crap" is only what's possible with cheap hardware today. Much better additive manufacturing processes exist - for a price, but price is going to keep on falling. And sure, if you want to build ten thousand wrenches a day, casting is obviously always going to be much cheaper than laser sintering. But, particularly considering the derivative of current technology, it is far from clear to me that, if I need 1000 different parts, a 1/100th share in the laser sintering printer at my local hackerspace is going to be pricier than a 1/10000000th share in 1000 foundries.
Torque is also a rather big consideration. Not everything you print on a 3D printer can handle the output you generate when tightening things (im)properly.
This was my first thought as well. I mean, you could make a "wrench" out of popsicle sticks and Elmer's, but it probably wouldn't work out so well for any real tightening. Curious what they used to make this, since I can't imagine a PLA-based ratchet being very useful (or anything not made from at least solid ABS)
Actually I wonder if this is economically viable today.