Piers Anthony 
Viscous Circle 

A warlike alien species is bent on destroying a pacifist alien species in this intergalactic adventure novel from the New York Times–bestselling author.Viscous Circle is a story about a strange and inhuman race of beings and an experimental attempt to transfer into creatures that seem only slightly sapient. They are ultimate pacifists who take the form of magnetic disks that float through space and simply demagnetize and destroy themselves when faced with an unpleasant thought. The bloodthirsty Solarians, in their desperate hurry to find the mysterious Ancient Site, are determined to wipe out the Bands, a strange and beautiful species whose society is an anarchy of peace. Only Rondl, the whirling green Band, can save his race, for he has a singular and awesome knowledge. But suddenly Rondl makes a shocking discovery about his identity—a discovery that may cost him his honor, his beautiful lover Cirl, even his very life.