I do believe that in order to be a person who can hurt others, you most likely were hurt as a child--assuming you were mentally balanced at the beginning. How you process that hurt as an adult, I believe, has to do with your personality type, if you had an adult in your life that was a positive influence (I had my grandmother), probably the degree of the abuse, and perhaps even your astrological sign--who knows.
I have never studied psychology aside from Psych 101 in college, but after nearly 3 years in therapy, I determined that I could have been a pretty good therapist. Aside from my own marital situation--which I read entirely wrong (but he was a very charming and deceitful n, who could sell ice cubes to Eskimos)--I am quite intuitive and can read people and situations well. My T seemed to agree with that.
Brigid