What Richard Posner Gets Wrong About Ideology

I'm reading an excerpt from Richard Posner's book How Judges Think for one of my classes, and I just came across the following passage:

For it is implausible that people are libertarians, or socialists, or originalists because libertarianism, or socialism, or originalism is "correct." They can't all be, and probably none is, except in severely qualified form. These isms, like religious beliefs, are indeed hypothesis-driven rather than fact-driven. Nothing is more common than for different people of equal competence in reasoning to form different beliefs from the same information. Think of how sophisticated people reacted to student riots protesting the Vietnam War in the late 1960s and early 1970s: some with horror, fearing social disintegration; others with exhilaration, hoping for transformative social change. They were seeing the same thing but interpreting it in different ways. Alternately they were reacting differently to the same information because of different intuitions, a kind of buried knowledge.

This strikes me as basically wrong. It's part of something that I think is basically right, namely a justification of judicial use of personal ideology in reaching decisions in legally ambiguous cases. But this gets something wrong about ideology, I think, and it's a common thing for people to get wrong. His example is instructive, because the "social disintegration" that some feared and the "transformative social change" that others hoped for were of course the exact same thing. It's just that some people wanted it to happen and other people didn't. So liberal radicals and conservative traditionalists weren't really "interpreting" the riots differently, they just differed on whether they liked what was happening.

My overall interpretation of ideological disagreements is that they're mostly about the fact that people have significantly different goals, values, and priorities from one another. Some of these differences are purely a matter of individual temperament and nature, differences in moral philosophy or what-have-you. Many derive from the fact that much of politics is a contest between the interests of different groups, and members of those groups have an understandable preference for their own side's interests. That's most of what was going on in the 1960s turmoil, for instance: society was set up in a way that put certain types of people in power and kept other types of people out of power, the disempowered types didn't like it, obviously, and started agitating to change it, and the people in power were not happy about the prospect of having their position challenged. You don't need any "different interpretations" to see why different kinds of people would react differently to the same events. It's like how people in Boston and in the Bronx had by and large opposite reactions to David Ortiz's various game-changing home runs in the 2004 ALCS: they were rooting for different teams. That's basically just a form of partisanship, which Posner rightly distinguishes from ideology, but in a sense they're not so different. I want the Mets to do well, on an essentially arbitrary basis; I want my own life to be a good one, for understandably simple reasons; and there are certain things that I would like to see happen on a purely moral basis. The origins of my preferences are different in each case, but the effect is the same: there's something I want to see happen, and I'm going to react to everything about the world based on how it affects those goals or desires.