Rhetoric that is polemical, that is caustic, that is ruthlessly extreme is potent in one sense yet vulnerable in another. It seizes attention and attracts acolytes; it is memorable and therefore memeable. But such strength can also be brittle. Writers who deploy it are susceptible to being cherry-picked and caricatured. They get enlisted in disparate causes and excerpted in college syllabuses. They become icons — whether to be smashed or revered.

I kept thinking about this paradox while reading “The Rebel’s Clinic,” Adam Shatz’s absorbing new biography of the Black psychiatrist, writer and revolutionary Frantz Fanon. In the decades since his death in 1961, Fanon has become that figure of double-edged distinction: an “intellectual celebrity,” as Shatz puts it, whose writing has been recruited for “a range of often wildly contradictory agendas” — secular and Islamist, Black nationalist and cosmopolitan — each trying to claim his uncompromising energy for its own.

For all his unwavering radicalism, he led a roving existence. He was born on the French Caribbean island of Martinique in 1925 and died, at 36, in a hospital in Bethesda, Md., in what he had called “the country of lynchers.” In between, he fought the Nazis in France, directed a psychiatric hospital in Algeria and eventually became a spokesman for that country’s National Liberation Front, known as the FLN, in its war against French colonial rule.

He was both a militant and a doctor, someone who promoted a “belief in violence” while also practicing a “commitment to healing.”

Fanon’s French secretary told Shatz that she hated seeing Fanon “chopped into little pieces,” arguing that those who tried to isolate one part of the man and his work “missed the indissoluble whole.” Shatz’s book is an attempt to restore a sense of fullness to Fanon, whom he largely, though not unconditionally, admires.

Fanon could be “vain, arrogant, even hotheaded.” In his first book, “Black Skin, White Masks” (1952), he derided homosexuality and wondered about “women who just ask to be raped.” During the last months of his life, while dying of leukemia, he wrote “The Wretched of the Earth” (1961). It depicted violence committed by colonial subjects against their oppressors as not only a matter of strategy, but also a psychological boon.

“Violence is a cleansing force,” Fanon wrote. (Shatz says that the line is better translated as “violence is dis-intoxicating.”) “It rids the colonized of his inferiority complex, of his passive and despairing attitude.” This was the kind of incendiary declaration that made some readers, including those who were politically sympathetic, recoil. The left-wing journalist Jean Daniel wrote a positive review in L’Express while confiding his revulsion to his diary: “a terrible book, terribly revealing, a terrible harbinger of barbaric justice.”

Shatz, the U.S. editor for The London Review of Books, is a mostly steady hand in turbulent waters. His chosen title highlights a side of Fanon that often gets eclipsed by the larger-than-life image of the zealous partisan — that of the caring doctor, one who was a “painstaking, diligent reformer in his day-to-day practice as the director of a mental hospital,” and, eventually, of a secret clinic for Algerian rebels.

Expelled from Algeria in 1957, after his hospital’s involvement with the rebels had been exposed, Fanon moved with his wife and son to Tunis, where he served as a loyal propagandist for the FLN as it became ever more authoritarian and paranoid. After a unit of the FLN murdered more than 300 villagers in Melouza for the crime of supporting a rival rebel group, Fanon held the party line, publicly denying any responsibility.

Part of what gives “The Rebel’s Clinic” its intellectual heft is Shatz’s willingness to write into such tensions. But sometimes he tips into generosity when something tougher is needed. He acknowledges feminist critiques of Fanon, who was persistently drawn to “hard men” and talked about needing to be a “god” to his wife. “Yet Fanon formed strong attachments with many of his female colleagues,” Shatz writes, a defense that gets perilously close to “some of his best friends were. …”

According to interviews conducted by the scholar Félix Germain for his 2016 book “Decolonizing the Republic,” Fanon would publicly hit his wife. Shatz steers clear of these disturbing allegations. Maybe his research debunked them, or called them into question. If so, it would have been good to know.

Because, of course, violence is a core part of “The Wretched of the Earth,” something that Shatz addresses head on, offering a smart, careful reading. He blames Jean-Paul Sartre’s notorious preface (“Violence, like Achilles’ spear, can heal the wounds it has inflicted”) for fixating on the book’s first chapter, “On Violence” — glorifying carnage without heeding Fanon’s call to channel such impulses “into a disciplined armed struggle.” Shatz directs our attention to Fanon’s last chapter, which includes wrenching case studies from his practice, involving both victims and perpetrators of violence. These show that even as Fanon wrote messianically about anticolonial violence, “he did not expect the psychological damage to be easily repaired.”

Shatz points to this “striking ambivalence” in a work of otherwise “militant self-certainty.” He is right, even if he emphasizes it more than Fanon’s book does. When a text begins with a lyrical exaltation of decolonization’s “red-hot cannonballs and bloody knives,” ending it with some case studies does little to tamp down the blast radius. Violence, whether in word or in deed, overwhelms. It crushes ambivalence — after all, that’s exactly what violence is supposed to do.