a normal human have every traits and behaviour inside him. people who says there are non violent manifest violence in other fields, sometimes with unexpected behaviour.
for example I considered myself as calm and everyone who knows me agree with this statement. but recently I came to see my dentist and he said that my teeth is severely damaged because I have this tendency to grit my teeth to evacuate my stress..
I believe that you already manifest dark traits in your life in a certain way, because if you're suppressing it, one day it will explode.