Question: What do Whittaker Chambers, Richard Nixon, John Roberts, Elena Kagan, Bill Clinton and Bob Dylan have in common?

Easier question: What do Judas, Benedict Arnold, Chambers, Nixon, Roberts, Kagan, Clinton and Dylan have in common?

Answer: All of them have been denounced as turncoats. A former communist, Chambers repudiated communism. Nixon went to China. Roberts, nominated by President George W. Bush, voted to uphold an important provision of Obamacare. Nominated by President Obama, Kagan voted to strike down an important provision of Obamacare. Clinton signed the law that ended welfare as we knew it. Dylan went electric, abandoning folk music for rock ‘n’ roll.

Disloyalty is not a virtue, and traitors rank among history’s worst villains. But societies need turncoats. In authoritarian nations, turncoats may be freedom fighters. In highly polarized democracies, turncoats are indispensable.

We need more Nixons going to China. We need more Dylans going electric.

In politics, turncoats make sensible compromises possible. If Democrats and Republicans are sharply divided on a question of economic policy and no one is willing to break ranks, an agreement might be unachievable.

The parties might be at loggerheads even if (as is often the case) some members of both parties privately believe that the views of the opposing party have merit. A single turncoat, abandoning the party line, can embolden members of both sides to say what they really think — and ultimately spur reasonable outcomes.

Turncoats also break down echo chambers. If conservatives or liberals are listening only to those on their side, they tend to become more confident, more unified and more extreme. The most serious problem with self-sorting is that it produces both error and dogmatism. It can severely impede learning — especially because those on the other side are so easy to dismiss.

Because of their own allegiances and history, turncoats are much harder to disregard. If Nixon goes to China, and if Clinton supports welfare reform, they can make people question beliefs that have been able to persist only for one reason: Inside the echo chamber, everyone shares them.

Turncoats are often independent thinkers, and they promote independent thinking in other people. That is a public service because on hard questions it is tempting to ask not about the merits, but about the views of your fellow believers — your party, your church, your group, your team. And some disturbing evidence shows that Republicans and Democrats are willing to suspend their own thinking, and to put aside their own independent views, after they learn about the opinions of their party. By eliminating internal unanimity, turncoats encourage people to get off automatic pilot and to think for themselves.

When Roberts voted to uphold the healthcare law, many conservatives dismissed him as a turncoat and as a coward. But it is likely that at least some of those who admire him, and usually agree with him, have been considering the possibility that he was correct.

It goes without saying that leaders shouldn’t betray their constituents or their colleagues. But in some cases, it is no betrayal, and it is neither cowardly nor a capitulation, for leaders to conclude that their constituencies and colleagues are wrong. Turncoating can be an act of exceptional bravery.