Slowly, but surely, robots (and virtual ’bots that exist only as software) are taking over our jobs; according to one back-of-the-envelope projection, in ninety years “70 percent of today’s occupations will likewise be replaced by automation.” Should we be worried?

Kevin Kelly, “senior maverick” at Wired magazine, and source for the above guestimate, says we shouldn’t. Instead, argues Kelly, in a Utopian piece titled “Better than Human,” we should welcome our new robot overlords. “They will do jobs we have been doing, and do them much better than we can. They will do jobs we can’t do at all. They will do jobs we never imagined even needed to be done. [But] they will [also] help us discover new jobs for ourselves, new tasks that expand who we are.” People have lost their jobs before, and everything turned out fine:

Two hundred years ago, 70 percent of American workers lived on the farm. Today automation has eliminated all but 1 percent of their jobs, replacing them (and their work animals) with machines. But the displaced workers did not sit idle. Instead, automation created hundreds of millions of jobs in entirely new fields.

If history repeats itself, robots will replace our current jobs, but, says Kelly, we’ll have new jobs, that we can scarcely imagine:

In the coming years robot-driven cars and trucks will become ubiquitous; this automation will spawn the new human occupation of trip optimizer, a person who tweaks the traffic system for optimal energy and time usage. Routine robosurgery will necessitate the new skills of keeping machines sterile. When automatic self-tracking of all your activities becomes the normal thing to do, a new breed of professional analysts will arise to help you make sense of the data.

Well, maybe. Or maybe the professional analysts will be robots (or least computer programs), and ditto for the trip optimizers and sterilizers. A quick Google search reveals any number of Web sites like aspjj.com (manufacturers of automated endoscope reprocessors) and wh.com (with their Autoclave Lisa, a fully automatic water-steam sterilizer). There’s no reason to think that the delicate profession of robosurgery will advance ahead of the already well-developed field of robosterilization, hence there’s no reason to think that the new profession that Kelly envisions will ever materialize. “Trip optimizer” is a similar red herring; Expedia and Kayak have already squeezed out most of what travel agents do, and the industrial-strength time-and-energy optimization of places like FedEx has long since been largely automated. The only thing left is the data analyst, but there are already dozens of new start-ups like Jeff Hawkins’s Numenta that aim to do just that, analyzing complex data in real time, more efficiently than humans can. I, too, like the idea of new technologies opening up new jobs, but every time someone makes a specific suggestion I get more worried, not less.

One possibility is that it won’t matter. Even if most of our jobs disappear and new ones can’t be found, productivity will grow; the overall pie will get bigger. Perhaps it won’t matter if some people, even a lot of people don’t have jobs. In Kelly’s optimistic vision,

Everyone has personal workbots…at their beck and call. Imagine you run a small organic farm. Your fleet of worker bots do all the weeding, pest control, and harvesting of produce, as directed by an overseer bot, embodied by a mesh of probes in the soil. One day your task might be to research which variety of heirloom tomato to plant; the next day it might be to update your custom labels. The bots perform everything else that can be measured.

But there is a darker possibility, too, which is that some people will own workbots before other people do, and that the people who lack workbots won’t be able to keep up with those to do. As Paul Krugman put it on Wednesday, “Smart machines may make higher G.D.P. possible, but also reduce the demand for people—including smart people. So we could be looking at a society that grows ever richer, but in which all the gains in wealth accrue to whoever owns the robots.” If you are a subsistence farmer, there is no way that you will be able to compete with your neighbor who owns one. Personal workbots could, some day, be like cars or cell phones, ubiquitous tools that almost everyone could afford, but they could also be like factories, affording new wealth for the owners, while others are stuck with shovels and seeds. For centuries, it has always been the case that some new jobs are eliminated by technology, while others are created. It’s hard to parse out exactly the role that technology has played, but as Erik Brynjolfsson and Andrew McAfee note in their superb recent book, “Race Against the Machine,” over the last decade throughout the economy, there has been a drop in the employment-to-population ratio and a drop in median wages, and many of the people who lost jobs couldn’t find new ones that paid as well as the ones that they lost.