Indifference could possibly be the most fatal of our emotional spectrum. The inability to summon any emotions or empathy, the inability to respond to any entreaty of assistance or compassion.
Because with hate, it still is nevertheless a form of passion. The subject in matter mattered sufficiently to incite hatred in the heart.
We all know the stereotypical premise of all martial art movies. Ie. To avenge a loved one's death, to never sleep untill the perpetrator rots in hell etc. That is hatred, and hatred usually comes with revengeful overtones. We could say the avenger is passionate towards the murderer. Passion is still passion regardless if it was malicious or benevolent.
But indifference, one shall not even bother.
Obviously love is not a subject to be covered here.