What is the opposite of good? Evil!
Jesus and Paul taught us to deal with evil by doing good. If we don't do that and instead try to follow our own instincts, what do we attempt as the answer to evil? If it is not good which we use to answer evil, it must be the opposite of good that we use instead. The opposite of using good against evil is using evil against evil.
In doing so I try to be so evil in return for your evil that you suffer intolerably. How's that been working?