Writing a Conflict in a Utopian Story

(MINOR SPOILERS: Best to read after reading The Alternate History of the Decline and Fall of the Roman Empire)

Every plot needs a conflict, and every novel needs stakes. But how can you write a conflict into a utopia? What kind of struggle would a protagonist face in an alternate universe 1000 years more advanced than our own? In writing The Alternate History of the Decline and Fall of the Roman Empire, I was so clear on the central message and theme of progress throughout history that I comfo...