We are to love each other, right? It's one of Jesus' greatest commands ("love your neighbor as yourself"). But is there ever a time, place or target where our most noble emotion could be hate, and our most noble action would be to attack?
If that's ever true, then I would guess a Christian to answer it is when we are directly fighting evil itself. In the 21st Century we don't always know how to label something as 100% evil, but we look back on the past and claim that some people (Hitler, Manson) or actions (genocide, murder) may qualify.
If we go back farther, though, to New Testament writings, we see that Jesus and his disciples encountered demons during their ministries. Demons! Surely if anything was to qualify as 100% evil, then it has to be these direct servants of Satan.
One of these encounters was recorded in the book of Mark (Chapter 5) with a demon called "Legion". But instead of Jesus battling this evil spirit with aggresiveness and attack, he does three amazingly graceful things:
1) Asks for the demon's name. This isn't to gain power over Legion -- it was already established that Jesus had that power without needing to know the demon's name.
2) Grants Legion's request that he not be cast out into "the pit". We're not sure what that means, but it didn't sound good, and Jesus spared Legion that fate.
3) Grants Legion a second request, that he be cast into a herd of pigs.
Why would Jesus show kindness and grace to a demon? Is there any possible advantage to be gained by this, or any possible different fate for Legion? Does a demon retain the hope of changing sides?
And applying to today, if Jesus showed kindness to a demon, exactly when do we have license to be angry and vengeful in the name of fighting evil?