... is to enact revenge. Take control of a power relationship, and exercise this power to the detriment of others.
Victims of any kind of abuse very often cannot do this with their abuser. The empathetic ally is then turned into a stand-in for the abuser, because - by definition of the binary distinction of X/non-X - they are part of the abuser's group. And, being empathetic, they offer themselves up.
I very much understand the coping mechanism here. We all fall into such patterns, I think.