I think there's several separate issues: Krugman correctly points out that work disincentives are different from job destruction. However there are different kind of work disincentives: it is certainly hard to view people working _just_ for healthcare (as opposed to switching jobs, retiring early, or starting their own business) as something positive. By all means, disentangling healthcare from employment is at least a worthy goal -- there are many artificial reasons which currently make non-employer health insurance (and non-insurance health care) far more expensive than would otherwise be.
On the other hand, the individual mandate and increased price of even the most basic catastrophic coverage does seem to cut into disposable income, which (in a sense) has the equivalent effect of huge marginal tax hike: essentially as the salary increases, essential benefits decrease (no eligibility for food stamps, subsidizing housing, or subsidized healthcare), while taxes increase. Incentive to do anything other than get by decreases, strong incentives are created to cut out other "unavoidable" payments such as by moving to places with less expensive housing costs, even if at the cost of less employment opportunities. Replacing the system that offers increasingly little to honest working poor(1), but imposes regressive mandates to fund what are essentially transfers from working classes to middle-class senior citizens (e.g., medicare and social secure) with a a universal basic income (funded through income tax or perhaps a Georgist "rent tax") would help, but making it a political reality may be tricky but feasible ( see here for an interesting analysis from a "left-libertarian"/classic liberal perspective: http://bleedingheartlibertarians.com/2014/01/the-positive-po... )
This does not automatically imply that various "mandates" of are always bad policy, the job of policy advocates should not be to hand-wave issues, but to present them in a way such that the public could make an informed choice. There are many times where Krugman does an excellent job of this (indeed, I'd imagine he rightly sees this as the very point of his NYT column); yet, it's odd that while Tyler Cowen (another trained economist) discusses this topic in a great deal in Great Stagnation and Average is Over, Krugman does not mention this and talks about what is really a related, but separate (even if important) matter of income inequality. Honestly, I don't see how income inequality (which is a serious danger for many reasons -- I don't mean to handwave it) has a role in this: if we raised the salary of teachers in Bay Area to that of software engineers, these salaries will still remain minuscule compared to that of top CEOs, but does anyone doubt that this would greatly increase teachers' job satisfaction? The problem with low pay isn't that someone is paid higher, the problem is that low (or no) pay makes life extremely stressful as basic needs and rudimentary wants are harder to fill: never mind being able to send kids to college, it's more about being able to afford a place where kids have a room to themselves while still having room to grade class papers after work -- one can't afford this on a teacher's salary in most parts of Bay Area.
(1) This is what irks me a lot about the debate on this topic. It's one thing to argue that welfare programs are wrong because taxation is wrong (then your job is to prove that taxation is wrong), but if taxation is wrong why not first cut programs that impose a greater tax burden? Military and medicare spending each cost more than food stamps and don't seem especially under-funded, yet it's the food-stamps program that got cut.
