This is another great article by the BBC, and the video is worth watching. This is a former white-supremacist talking about how he had a change of heart due to the kindness of others.
It reminds me of a famous quote from the Dhammapada, translation by Ven. Acharya Buddharakkhita:
5. Hatred is never appeased by hatred in this world. By non-hatred alone is hatred appeased. This is a law eternal.
My belief is that many such people who dehumanize and abuse other people are really suffering from self-hatred, but are unable to see it.
One of the things I’ve learned from Yogacara Buddhist thought is how the mind projects itself onto the world around it. Thus, a mountaineer and an artist will view the same mountain differently even when standing right next to one another. In the same way, the recurring mental habits in one’s mind create a feedback loop that in turn distorts the world around them according to their disposition.
If a person is filled with self-hate and obsessed with rage, frustration and a sense of inferiority, they will inflict pain and humiliation on others, living by an us-versus-them mindset. This will in turn reinforce the existing mental habits over and over.
But at the same time, the Buddha taught not to get caught up blind reaction toward such people. The first instinct is to fight back and punish such people. Fight violence with violence in other words. However, as the article above shows, it may be more effective to rely on a combination of truth (not paranoia and lies) and goodwill to counteract such people. If those people can find personal healing, they may change their ways.
As the Lotus Sutra teaches, all beings are capable of becoming buddhas, they just need the right trigger.