To defeat people who hate without restraint, you must take up some of their hatred and so become a little unlike yourself. They feel no such conflict and can destroy you without qualms. The danger is becoming so much like them that they win even in defeat.
We speak as if we face the future with the past at our backs, but nothing exists yet in the future. One could die at any minute, so we really face a void. Only the past, held in memory, can actually be seen.
Trying to get away from a painful past keeps you tied to it, like a man who takes a girlfriend to forget his wife. Sealing off old boundaries is hopeless, because everything touches everything else. A beginning never disappears, not even when things end.
In wartime, blame rarely falls cleanly on one party. Chance, small decisions and neighbourly ties tangle together, so that the guilty and the innocent overlap. The damage keeps working between neighbours and spouses for decades.
Someone who acted violently against oppression argues that condemning the act means wishing humanity had never existed. If one innocent child's death outweighs all the world's love and goodness, no human history could be justified. The argument does not make the cost disappear, but it changes how the act must be judged.