The iron man works like the straw man. You take an argument (or an arguer), distort his argument, pick an urepresentative feature of his argument, or you invent an argument the person does not make all in order to make the argument the person makes appear to be stronger than it is. This has the related effect of making the critics look unfair, unhinged, or shrill. More importantly, it may serve to cover over the real vices of someone's position.
Oftentimes strengthening an argument serves both practical and epistemic ends. We're better off if everyone is better at arguing and if we're considering better arguments. However, in the case of ironmanning, strengthening arguments may make us worse off, because we don't consider for example what is actually being proposed by someone, or the worst-case-scenario effects of someone's view.
I posted an example of this yesterday from Krugman. Here is another example from Krugman.
But the “centrists” who weigh in on policy debates are playing a different game. Their self-image, and to a large extent their professional selling point, depends on posing as high-minded types standing between the partisan extremes, bringing together reasonable people from both parties — even if these reasonable people don’t actually exist. And this leaves them unable either to admit how moderate Mr. Obama is or to acknowledge the more or less universal extremism of his opponents on the right.
Enter Mr. Ryan, an ordinary G.O.P. extremist, but a mild-mannered one. The “centrists” needed to pretend that there are reasonable Republicans, so they nominated him for the role, crediting him with virtues he has never shown any sign of possessing. Indeed, back in 2010 Mr. Ryan, who has never once produced a credible deficit-reduction plan, received an award for fiscal responsibility from a committee representing several prominent centrist organizations.
Let's consider it a factual matter as to whether the presentation of Ryan's views is accurate. It likely is, IMO, but that's not the point of this post anyway.
There would be much to gain by the intellectual exercise of pretending there are Republican moderates. But let us say they do not exist. Pretending that they do, or recasting very extreme views in moderate tones, is very harmful to our public discourse.
The straw man unjustifiably excludes reasonable views from consideration by pretending they're unreasonable, the iron man unjustifiably includes unreasonable ones by pretending they're reasonable.