Was Kunta Kinte's (in "Roots") pride as a Mandinka Warrior helpful or harmful during his lifetime?

It depends on one's perception of what is "helpful" and what is "harmful" in a slave system. 
Kunta Kinte (later, "Toby") insisted not only on retaining his identity, symbolized by his stubborn insistence on refusing his new name—but also identified as African. He never lost his sense of history; he did not identify with his slave status. His ability to remember his history created the possibility for Alex Haley to tell this story—his family's story—which is the history of many Black Americans and a history of America.
His pride was "harmful" because it led to severe abuse. The best-known scene in the miniseries version of Roots is when young Kunta Kinte, played by LeVar Burton, is whipped repeatedly for refusing to accept the slave name Toby. Later, Toby (played by John Amos) has his foot cut off to prevent him from running away. Punishments such as these were not unusual. There were also slave masters who inflicted cruelty on slaves simply because they could. So, there is no guarantee that Kunta Kinte's compliance would have resulted in less harm. A slave's health and life were maintained at the whim of a master.