How to Make a Monster
Violance is easy to cure from practical point of view. It's just so scary to do it practically.
I agree of what Stef said on this one. A sadist born from unfortunate events in his/her timeline. Not in a night but a lifetime, that's what it is that shape someone's mind. Of course, it's ceteris paribus; a drastic event could create traumatic can take it out in an instance.
Now, the real cure of it is compassion. Meaning, to swallow our pride and try to forgive the monster. A mere stare, a spit in the face, mockery and any humiliating would not effective. Any swearing would just make the monster invulnerable.
Because the monster is not the person. It is the state of mind of feeling troubled over the person's endangered existance. Everyone have the self-mechanism to defend one's own existance. By any mean necessary! A compassion is to protect the one's existance and to protect ourselves against its rampage.
An existance, either by this world or (to whom believe) other world, is a crucial matter for each human. It is a grand question of any person in the world. Some might try to define that we are purposeless, just some random biological compound of nature. But, by answering the question, those some are already in that question area. Isn't that they also seeking for their purpose?
A purpose. You can't give that to people via hatred. You can't change them by made them suffering. And simply, a lost person would not listen to people when the person feel like being dominated. Nobody loves to be dominated by others. Everyone wants control, even if the control is being other's command.
Yes, we want certainty in this uncertain world. Random things would prefered as long it is in the expected area of mind. We strive to change and adapt to change. Yet, we would want that change happens not beyond the area of our acceptance.
That's why, there is a hard way for people to change. You could not change a person's mind in a night unless with a drastic measure. Unfortunately, a drastic measure of making monster is easy to find, but a drastic measure to cure a person is hard. It takes time for people to change into a better man. An alarm could turn on in an instance, but you must take the time and procedure to take it off.
Now, the real question is: can you forgive someone who hurts you? Takes time, though.
Thus, easy to cure practically, yet hard to do it practically.