Sunstein’s forceful stance matters because he’s a respected scholar (he teaches law at the University of Chicago) and because he’s a restrained, thoughtful liberal (he clerked for Thurgood Marshall, but cites Sandra Day O’Connor’s minimalist approach as a model). Ideology does affect the way judges vote in important cases, Sunstein has argued to senators who worry that it’s unseemly to oppose a nominee simply for being too far to the right. Now he has done the research to prove his point and then some.

Most of Why Societies Need Dissent isn’t about partisan politics. It’s a survey of social science research about group conformity, aimed at showing why the pressures exerted by groups often lead to bad or ill-informed decision making. As a counterpoint, Sunstein demonstrates the value of naysayers, particularly those who offer new information along with wagging fingers. The book is written in the crisp, level tones of a lecture–the Oliver Wendell Holmes Lectures at Harvard Law School, to be exact, which Sunstein gave in February.

Still, Sunstein’s concern about the Bush nominations explains the book’s timing and its most original contribution: a study of the voting patterns of appellate judges. Along with two other researchers, David Schkade and Lisa M. Ellman, Sunstein looked at thousands of votes cast by these judges, who hear appeals in panels of three. As you might expect (unless you’re a senator determined to stick your head in the sand), he and his colleagues found that in ideologically contested cases, Republican appointees tended to vote along more conservative lines and Democratic appointees tended to vote along more liberal ones. More strikingly, the judges were significantly influenced by the political affiliation of their co-panelists. For example, Democrats (to use Sunstein’s shorthand for judges appointed by Democratic presidents) voted to strike down affirmative action programs only 28 percent of the time between 1980 and 2002. But a Democrat who sat on a panel with two Republicans voted to invalidate the programs in 45 percent of cases. The votes of Republicans were inversely affected by their co-panelists: They voted against affirmative action programs 57 percent of the time overall, but only 32 percent of the time when they sat with two Democrats.

Sunstein’s study showed that split panels also moderated decision-making in cases involving sex discrimination, sexual harassment, the liability of company directors for corporate wrongdoing, and industry challenges to environmental regulations. Capital punishment and abortion cases were two interesting exceptions. Judges don’t bend their convictions in deference to each other’s views when questions of life and death are at stake, Sunstein surmises.

What to make of the judges’ malleability in other areas? Sunstein gently suggests that judges are as vulnerable to peer pressure as insecure teenagers. An all-Republican or all-Democratic panel “tends to go to extremes” because its members reinforce each other’s predilections rather than challenging them with competing arguments. On a split panel, by contrast, an outlier judge can act as a whistleblower by forcing his colleagues to adhere more closely to legal precedent.

Given the title of his book–not to mention its dedication to Judge Richard A. Posner, the iconoclastic conservative who is one of Sunstein’s faculty colleagues–it’s no surprise that the author cheers for these dissenters. In Sunstein’s view, cozy unanimity ill serves the law by narrowing the accepted grounds for discussion. The real danger of the lockstep conservatism of the Bush nominees is that they’ll rub out counterarguments from the left by wearing down the remaining Democratic minority. After all, Sunstein writes, the judges he studied were “behaving as ordinary people do,” and ordinary people “do not like to be lone dissenters.”

On Sunstein’s ideal appellate court, judges with a mix of perspectives would debate each other in each case, increasing the chances that a wide range of arguments would be taken seriously. That sounds almost unassailably reasonable–until Sunstein gets to his quite radical proposal for reform. Instead of randomly assigning judges to panels, as is customary, he thinks the chief judges who make the assignments should deliberately split the panels between Republicans and Democrats.

This is a direct attack on the traditional notion that judges merit special authority because they apply neutral principles. It means abandoning the idea that judges can ever be reliably apolitical. So, it’s sure to be condemned by judges and academics, liberals as well as conservatives.

But Sunstein is unlikely to be fazed by the criticism because his proposal lines up perfectly with another reform concept he’s long supported: “deliberative democracy.” The best way to guard against runaway extremism in society at large, Sunstein thinks, is to sit people down together for reasoned and informed debate about fundamental questions of policy and morals. The idea is to offer an alternative to a liberalism that’s myopically focused on individual rights and a conservatism that puts too much faith in market competition between interest groups. Sunstein approvingly cites a study in England which found that when people with different beliefs read factual material about an issue like crime prevention and then talked about it, their views often merged toward the center (actually, toward the center-left).

There’s something wistfully pin-headed about deliberative democracy–it sounds a lot like law school. The most important factor in the British study, Sunstein suggests, was that the participants were presented with “a set of written materials that contained detailed arguments for both sides and attempted to be balanced.” For most Americans, balanced reading material isn’t likely to replace TV attack ads as a main source of political information anytime soon. But reading through opposing briefs is already at the top of an appellate judge’s job description. Sunstein is right that deliberative democracy is within the reach of the courts. He’s also right that as the out-of-power party, the Democrats have the most to gain from preserving the courts’ ideological mix.