Hatred does not ever cease in this world by hating, but by love; this is an eternal truth. Overcome anger by love, overcome evil by good. Overcome the miser by giving, overcome the liar by truth. - Shakyamuni BuddhaUsually in Buddhism, we talk about loving-kindness (or metta). But I'd like to talk about loving-anger. So, two points about this quote:
Zen Master Seung Sahn, when speaking about anger, said there are different types. First there is the type that blinds you so that you don't know what you're doing. But there are others as well, like the anger a parent has when their child runs out into the street. This is an anger that comes from love and that can be used as a tool by the loving. Sometimes, people think that being peaceful means never being angry, but this is just attachment to the idea of peace. Better to say that being wise means using anger rather than being used by it. For those of us who aren't Buddhas yet, there isn't necessarily specific advice to give (other than hard practice). For some, angry karma is a real problem, and they should try not to give in to it; but that's not applicable to everyone.
If you do hard practice, over time you will notice that the quality of your anger changes. If you come to understand the idea of loving-anger intellectually, however, you will never understand it. The intelligence easily deceives us, so that knowing about different types of anger only enables us to better delude ourselves into thinking our anger is born of justice. So, many people easily think one side in a war is better than the other side, and that to be angry on behalf of that side is to be righteous and the same as being on the side of peace. But this is just thinking. This righteous anger is not peaceful anger. It's not loving anger.
Both sides in the Israeli/Palestinian conflict do this -sometimes doubly deluding themselves to think that their anger is more loving that "their" anger- so anger and pain on both sides grow. Together, the Israelis and the Palestinians make conflict karma. The only way to overcome that is through peacefulness and love.
When Paul McCartney went to Israel (facing death threats from some who think that no one should ever show love to Israelis), he sang John Lennon's song, "Give Peace a Chance." The crowd, with his encouragement, sang along to the chorus. And afterwards, Sir Paul simply pointed out to them what they had said.