What caused Superman to fight crime?

Answer 1

He considers it his responsibility to protect the world from danger having all his super abilities. It is believed he learned of his good ways from being raised by the Kents as other Kryptonians used their powers in attempting to rule the world.

Answer 2

Clark Kent was raised to be a good boy and realized his powers were a huge responsibility rather than an advantage to show off for personal gain. It is believed he would have turned out like General Zod if he had been raised on Krypton instead of Earth by the Kents.