It seems to me that when readers declare that some piece of economics commentary is “wrong”, they often confuse three different notions of wrongness, which are neither intellectually nor morally equivalent.
First, there’s the ordinary business of expressing a view about the economy that the reader disagrees with – e.g., “Krugman is wrong, because the government can’t create jobs”; or, if you prefer, “Casey Mulligan is wrong, because we’re suffering from demand problems, not supply problems.” Obviously it’s OK to say things like this, and sometimes the criticism is correct…. [There's] wrong about being wrong in this sense: people will disagree, and that’s legitimate.
Second, and much less legitimate, is the kind of wrongness that involves making assertions that are logically or empirically indefensible. I’d put the Cochrane/Fama claims that government spending can’t increase demand as a matter of accounting in this category; this is a basic conceptual error, which goes beyond mere difference of opinion. And economists who are wrong in this sense should pay a professional price. That said, I don’t think it’s realistic to expect the news media to be very effective at policing this kind of wrongness. If professors with impressive-sounding credentials spout nonsense, it’s asking too much of a newspaper or magazine serving the broader public to make the judgment that they actually have no idea what they’re talking about.
Matters are quite different when it comes to the third kind of wrongness: making or insinuating false claims about readily checkable facts. The case in point, of course, is Ferguson’s attempt to mislead readers into believing that the CBO had concluded that Obamacare increases the deficit. This was unethical on his part – but Newsweek is also at fault, because this is the sort of thing it could and should have refused to publish.