I'll counter some of your counter points :).

+ 3-D printers aren't economical — Something like a drywall anchor takes a couple seconds to produce in a traditional injection molding process. It would likely take 15-30 minutes using an FDM 3-D printing process and even longer using a higher resolution SLA system.

It depends what you're creating to determine how economical it is. A drywall anchor is obviously going to go down the mass production path as you need more than just one drywall anchor. A personalized iPhone case (with your name on it, to differentiate it from all your friend's iPhones) is a different story. It's significantly more expensive to mass produce truly personalized items ('truly' in the sense that the structure of what you're creating has changed - you could slap a sticker with your name on it, but that's a sticker on a case, not a personalized case).

I have an FDM printer, I'll print this (http://www.thingiverse.com/thing:5489) out and report back when it's done (it'll probably be about 15 minutes, but my printer is slow (40mm/s, some get up to 150mm/s). (before I was done writing this comment, my machine finished printing the drywall anchor - 10 minutes and 10 seconds of print time, see the picture here - http://imgur.com/a/iPnNx, it broke when I tried to use it (need to scale it up a little bit)).

The SLA - FDM argument isn't true, a higher resolution should take longer, but SLA systems can print 2D planes at a time (unless they raster, in which case their print head speed is limited by how quickly their mirrors can move), speeding up the process a LOT. I can set my FDM to a .01 layer height, but it would take 25 times as long to print something as opposed to using a .25 mm layer height. I can just sand the part in 5 minutes and print something new.

+ Print-on-Demand hasn't taken off on books, why will it with physical goods? Print-on-Demand technology has been available for the better part of a decade, but Barnes & Noble and Borders never saw an opportunity to implement it. Again, this comes down to speed. For undifferentiated products, it will always be faster to mass produce.

Your last sentence here is the reason 3D printing (if it does) will succeed. My sister broke the knob for her oven. It's an old oven, the company wanted $47 to replace the knob. They had a guy come over with a bunch of knobs, and for some reason none of them fit. I printed one, first try, and wham, it fit perfectly. No more pliers to turn the oven on! Now you wouldn't buy a printer specifically for this use case, but when my nieces and nephew come over and I can print them a glider airplane (that he took to show and tell) and a wand in the time it takes them to watch a show, that's pretty cool (they get a kick out of watching the part develop).

My sister brings me lots of stuff to fix (some I can, some I can't). I haven't done it yet - but having the ability to whip up obscure parts for 'disposable' toys allows them to stay alive a little longer. With a 3d printer, I can fix almost any mechanical problem you have with your toys.

It's not for everyone, but for the people who use them it gives them amazing abilities they did not have before. I don't have much money, so I can't get nice sheets of acrylic, wood, whatever to shape something out of, but I have a spool of plastic and can print almost anything.

+ Even taking the argument at face value that 3-D printing will help digitize inventory and create the same pressures that digital media did, I think more efficient mass production, rather than 3-D printing will be the likely case. Zara can produce limited runs of high fashion clothing and get them into malls all across the US in 2 weeks. Protomold makes low cost, small run injection molding accessible. We'll likely see more of this rather than fleets of MakerBots.

Thanks for the protomold link. I made a 3D printer for a product I want to make (hoping I'd be able to print some cases for it), but it's too slow for how many I want to sell. I'm debating 1/4" plywood, or injection molding. I think (as I have no money yet) wood will be the first run, but then I'd like to injection mold my parts (3D printing helps here too (or rapid prototyping), I can make sure my parts work before spending $1500 on a mold and crossing my fingers).

In terms of the actual article, I think 3D printing will compliment big box purchases, providing a market where add on customization (in many ways like a tattoo shop - you come in once, talk about what you want, set up a date when you want to get it done, and come back and the part is fixed / modified).

3D printing is what you use when you want something, but don't have a good way of getting it.