At my prodding, Sean Carrol considered the differing public treatment of physicists and economists:

In the public imagination, natural scientists have figured out a lot more reliable and non-obvious things about the world, compared to what non-experts would guess, than social scientists have. The insights of quantum mechanics and relativity are not things that most of us can even think sensibly about without quite a bit of background study. Social scientists, meanwhile, talk about things most people are relatively familiar with.

Hey, economists can talk obscure technical jargon just as easily as physicists. We don’t actually do that so much in public, because the public respects us less. Talking more technically wouldn’t make the public respect us more.

On the very basics of their fields (the Big Bang model, electromagnetism, natural selection), almost all natural scientists are in agreement. Social scientists seem to have trouble agreeing on the very foundations of their fields. If we cut taxes, will revenue go up or down? Does the death penalty deter crime or not? For many people, a lack of consensus gives them license to trust their own judgment as much as that of the experts.

Revenue if tax cut and crime if death penalty aren’t remotely near the foundations of economics. We can’t talk about economic foundations in public without using obscure technical concepts the public won’t tolerate. Physicists are more allowed to talk their foundations in public, as they are allowed more tech talk. (I’ll consider consensus issues below.)

The social sciences deal with fantastically more complicated subjects, about which it’s very naturally more difficult to make definitive statements, especially statements that represent counterintuitive discoveries. The esoteric knowledge that social scientists undoubtedly possess, therefore, doesn’t translate directly into actionable understanding of the world, in the same way that physicists are able to help get a spacecraft to the moon.

There is a final point that is much trickier: political inclinations and other non-epistemic factors color our social-scientific judgments, for experts as well as for novices. … When deciding where to place that trust, we rely on a number of factors, mostly involving the track record of the group to which the purported expert belongs, if not the individual experts themselves. So my advice to economists who want more respect from the outside world would be: make it much more clear to the non-expert public that you have a reliable, agreed-upon set of non-obvious discoveries that your field has made about the world. People have tried to lay out such discoveries, of course — but upon closer inspection they don’t quite measure up to Newton’s Laws in terms of reliability and usefulness.

The public is taught to credit physicists for all those physical things around them they enjoy, like cars, planes, phones, and skyscrapers. The public is not taught to credit economists for all those great economic institutions around them like markets, firms, cities, and industries. So naturally physicists are seen as contributing more. But is this fair?

Yes, economists were only a supporting influence in creating all those great economic institutions, unless we want to define all businessmen as economists. But similarly, physicists were only a supporting influence in creating all those great physical devices, unless we want to define all engineers as physicists. There were useful steam engines long before thermodynamics helped explain them, and it took far more than basic physics to get men to the moon, just as it took far more than basic economics to create modern industries. It is actually quite hard to say which discipline has been more useful overall to the world.

They key difference, I think, is that more interested parties see themselves as losing if the public listens to economists, and these parties therefore dispute economists in public. Such interested parties also influence individual economists, and so weaken within-economics consensus. In contrast, few care enough about what physicists say to dispute them in public.

The fact that economists are more disputed in public than physicists seem plenty sufficient to explain the differing public treatment of the two fields. Even if physicists did have a more “reliable, agreed-upon set of non-obvious discoveries,” that couldn’t explain the differing public treatment of the two fields for the simple reason that the vast majority of the public has no idea about such things. They don’t know about physical or economic discoveries, nor about how reliable or useful such things are. What the public mainly knows is that when physicists talk few disagree, but when economists talk lots of folks disagree, and each ordinary Joe is himself often tempted to disagree.

Now the fact that economists are more disputed does in fact give the public more reason to doubt what economists say. But this only justifies increased uncertainty, not swapping expert opinion for their own personal reasoning. The desire to believe that what is in your interest is also in the general interest can on average distort individual reasoning just as much as it can expert reasoning, if not more so. In both fields it is better to believe nothing, or believe the experts.