A follow-up: I think the main sign of poor economics discourse in Krugman's article is that he didn't even think it necessary to pre-empt your obvious counterpoint, thereby making his argument woefully incomplete. It would have been a lot more productive if he had added, "It wouldn't do any good to sell babysitting services below the coupon face value, because ____. This corresponds to ____ in the broader economy, which is bad because ..."
Also, I agree with Vladimir M.
Tangential, but a subject of some local interest:
Why Bitcoin will fail by Avery Pennarun. "The sky isn't red." Thesis:
I'm not sure I buy these and am not competent to evaluate his claims on 3., but would like others' critique.
L019: Bitcoin P2P Currency: The Most Dangerous Project We've Ever Seen by Jason Calacanis. A rather more enthusiastic viewpoint of the project:
The actual text contains many more caveats than the eye-catching selection of points above.