It’s sweet to be agreeable—but what a vibrant, healthy society really needs is principled troublemakers.

Those who dare to say “no” when it appears that everyone else is in agreement are rare and brave—and they make the world a better place, according to University of California, Berkeley psychology professor Charlan Nemeth. Her new book, In Defense of Troublemakers: The Power of Dissent in Life and Business, shows how everyone benefits when someone presents a thoughtful contrarian view.

Nemeth’s research in social psychology and cognition has shown that disagreement improves group thinking. “It’s a benefit regardless of whether or not [dissenters] hold the truth,” she argues. “Most people are afraid and they don’t speak up. Companies have that problem all the time. And the research really shows us that that even if it’s wrong, the fact that the majority or the consensus is challenged actually stimulates thinking.”

The professor has spent decades studying disagreement, looking at the behavior of juries, companies, airplane crews, and groups in general. Her work shows that a challenge to the general consensus generates necessary consideration and debate. This, in turn, improves decision-making, leads to more creative solutions, and even saves lives, for example in a criminal case where a defendant’s life or liberty may be at stake.

The American justice system relies on this kind of contrariness. If 11 jury members agree that the defendant is guilty, based on the evidence presented, and one jury member keeps holding out, the rest of the group is bound to get impatient and complain. Still, because they must reach a unanimous verdict, the group will have to reconsider the evidence and argue until all are convinced of a conclusion, based on facts. That’s a jury’s job, and doing it properly can mean the difference between incarceration and freedom, even life and death, for an innocent person.

Though it’s not easy being the disagreeable person in a group, standing up for your truth ensures that actual or self-appointed leaders and conscious or unwitting bullies don’t do damage to a process, project, person, or institution.

Dissenters seem like a pain. But principled troublemakers who challenge prevailing groupthink create more space for all. Nemeth told Quartz in an email, “We actually do others a favor because our dissent—provided it is authentic—stimulates them to think more broadly and deeply. Our groups make better decisions. We ourselves gain clarity.”

As for politesse, the professor is merciless, putting meaningful discourse above mere manners. She doesn’t think it’s better when everyone just agrees for the sake of general good feels. “We have to stop being polite if it means being dishonest about what we believe,” Nemeth says.

Nemeth offers these rhetorical questions, “ruminations” for your consideration. “Do we really want to spend our lives worrying about not offending, walking on pins and needles lest someone be upset with us?” she asks. “Have we lost our ability to know what we know and to engage in honest discourse?”

Hopefully, your answer is “no.” But please do feel free to disagree.