In a well-known phrase, the Buddha said, "Hatred can never cease by hatred. Hatred can only cease by love. This is an eternal law." We can begin to transcend the cycle of aversion when we can stop seeing ourselves personally as agents of revenge. Ultimately, all beings are the owners of their own karma. If someone has caused harm, they will suffer. If we have caused harm, we will suffer. As the Buddha said in the Dhammapada:

We are what we think.
All that we are arises with our thoughts.
With our thoughts we make the world.
Speak or act with an impure mind
And trouble will follow you
As the wheel follows the ox that draws the cart. . . .
Speak or act with a pure mind
And happiness will follow you as your shadow, unshakable.

Happiness and unhappiness depend on our actions.

--Sharon Salzberg, Lovingkindness

from Everyday Mind, edited by Jean Smith, a Tricycle book