Excellent post by Noah Smith examining the question of why so many people who aren't trained economists like to weigh in with views on macroeconomics. One reason, he suggests, is that people look at macro and see a modelling approach that doesn't seem terribly plausible, and they also see lots of macroeconomists disagreeing over fundamental points. What they see mostly looks like ideology dressed up to look like something else. As he notes,
There is the perception that macroeconomists don't understand their own subject. The Great Recession convinced a lot of people that macroeconomics hasn't solved any of the problems it was created to solve. Contrast that with physics or bio or chem, which have very obviously given us a lot of the awesome stuff that makes our society rich. In addition, you have very public and acrimonious debates between macroeconomists like Krugman, Cochrane, and Sumner. That convinces a lot of people that there is no consensus within macro, which in turn makes them suspect that macroeconomists haven't gotten any answers out of the Universe. If the experts don't understand anything, why can't the amateurs weigh in?
I am not annoyed by normal people's penchant for butting into macro debates (though the "Austrian" and "heterodox" people do annoy me, since they approach things in a tendentious rather than an inquisitive manner). I think it's natural. Sure, a lot of stupid stuff gets said, but let he who is without sin cast the first stone!
I would agree that this is the main reason. By chance, I came upon this post just as I was reading a speech given two years ago by Manchester economist Diane Coyle. She is by no means a heterodox renegade. In general, she argues that there's lots of value in today's economic theory, though not necessarily in macroeconomics. The problem there, as she see it, is pretty clear:
Macroeconomics – the study of how millions of individual decisions aggregate into economy-wide measures – is essentially ideological. How macroeconomists answer a question like ‘What will be the effect of cutting the budget deficit on growth next year?’ depends on their political views. This is not remotely a scientific area of the discipline.