OK: If I were you, I would compare Beowulf to a Special Operations US Army Soldier. If your teacher asked you to compare him to a doctor, question why? Beowulf was not out there to help ailing people: He was a natural-born leader whose comrade and right died and this caused a crisis in him, just like soldiers feel guilty about their comrades dying at war.
Beowulf came from an elite line- he understood the concepts of leadership, delegation, honor, duty- just like our soldiers are indoctrinated to understand. Beowulf fought evil, fell from grace for a while, accepted death, but kept on going. That brings him way aside from a doctor-though doctors are also heroes- and places him right along the lines of an American soldier.
Beowulf has plenty motives that are similar to those of a soldier: Avenging a dead comrade's fall, defending the country, respecting the King, settling the people, accepting the duty...those are great attributes that put him in line with the military-not to mention his leadership.
In all, if I were you, I would bring up the soldier comparison and argue the comparison to the doctor. The soldier comparison makes a whole lot more sense.