Why the decision to ignore Judith Curry isn't simple

Climate Etc. lead for much of yesterday with a post entitled "Why the decision to tackle global warming isn’t simple." It's mostly excerpts from a piece by Jim Manzi in the New Republic, which reiterates the Curry Fallacy: I don't know how much global warming there will be, or how destructive it will be, because of the huge uncertainties, but I do nevertheless know that the risk of it being highly destructive is small, and I know the costs of cutting emissions will be huge."

The common sense problem with the Curry Fallacy is, of course, that if you don't know what the risk is, then you don't know what the risk is.

Am I exaggerating dizzying illogic of all this? See for yourselves:

The starting point for such a consideration is to recognize that we are not certain how much CO2 humanity will emit, how much warming a given amount of CO2 will cause, or how much damage a given amount of warming will cause.  That is, we are concerned here with the inherently unquantifiable possibility that our probability distribution itself is wrong.

But:

The expected economic benefits of emissions mitigation do not cover its realistically expected costs.

 How can you know the benefit to be realized in preventing a certain amount of warming if you don't know how much damage the warming itself would cause? It makes no sense.

Unfortunate Mr. Manzi, who also writes for the National Review, has caught the habit of not only ignoring facts he doesn't like, but actively misrepresenting them and distorting the truth. His evidence for the above claim (that the expected economic benefits do not justify the costs of mitigation) is only this:

William Nordhaus, who heads the widely respected environmental-economics-modeling group at Yale, estimates (page 84) the total expected net benefit of an optimally designed, implemented, and enforced global program to be equal to the present value of about 0.2 percent of future global economic consumption.

 Although he just called Nordhaus "widely respected," and although Manzi is not an economist and has not done any of the calculations himself, he arbitrarily decides to multiple the costs of mitigation several times, to reflect unspecified "side deals" he's sure would push the cost skyward. Shame they didn't do that with their estimates on the cost of the Iraq war, eh? Anyhow, that is how he concludes, based on Nordhaus, the exact opposite of what Nordhaus wrote: Nordhaus said action will save three and a half trillion dollars, and Manzi concludes from that that mitigation is an economic loser whose costs will far exceed its benefits.

We can count our blessings: neither Curry nor Manzi deny that the earth is warming, or that humans are the cause, or that the resulting changes will be, at least to some degree, destructive. But they do  misrepresent serious research, and deploy the concept of uncertainty selectively, using it to justify ignoring projections they don't like, and ignoring it when they don't.