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Hmmmm. While I think it is true that both Solow and Lucas are pretty set in their views, Sargent has actually adjusted his somewhat over time. In particular, after spending some time at the Santa Fe Institute in the early 90s, he relaxed his support for rational expectations, while not completely abandoning it. His later view has been more along the lines of that in reality people use some form or other of adaptive expectations, but that over time they tend towards adopting rational expectations.
I suppose physicists can have a conversation about assumptions - "I don't believe the speed of light is an ultimate limit, gravity is not a constant, and pi has a finite number of decimals." If they did have such discussions, they could agree on testable (or non-) empirical implications, and it's hard to believe that they'd get very emotional about it. They can even discuss reasonably, these days, whether there are lots of different dimensions holding string theory together -- something totally untestable.
So, why was Solow so negative to rational expectations? After all, it's a testable assumption. As a working hypothesis, it has a lot going for it, and finding its limits should be thought of as an exciting scientific quest. To dismiss that by saying Grantchester is pretty haughty and may suggest a closed mind. Perhaps it made him think he's a philosopher, whereas Lucas was just a lousy statistician, lower than a dog. That's not an usual academic approach to dismissing critics, now is it? But should that be acceptable in economics?
Or is it that all economics is at heart a more emotional than rational discipline, that someone's "assumptions" are merely expressions of a desire to see the world as it ought to be rather than as it might really be? I fear that the latter explanation has more than a grain of truth. A lot of economists, especially these days, seem fearful of having their basic assumptions questioned. Just ask people what they think of "multipliers" and you're likely to get things thrown your way.
Maybe they just enjoy disagreeing for argumentative sake.