Studies have shown professional victims tend to have negative personality characteristics, most notably the Dark Triad. 

Then there is the matter of projection, the psychological mechanism wherein a person projects his/her own negative characteristics onto others. Thus, we see individuals call their opponents "fascists" while advocating and imposing censorship, calling for concentration camps for political opponents, engaging in the politicization of science and art, falsifying history, peddling propaganda, physically assaulting people having different viewpoints, and engaging in the indoctrination of children.

It is possible that you may not have heard of psychologist Stanley Milgram's famous experiment. Milgram's experiments on obedience to authority always had a political undertone, which he himself stated. He proved that a large majority of people would continue to engage in an immoral act when ordered by a person in authority, specifically administering increasingly painful electrical shocks to another person.