Arjuna raises a piercing question: O Janardana, what joy could we possibly gain from killing the sons of Dhritarashtra? Even though they are aggressors, slaying them would only bring sin upon us.
There is a deep tension in this verse. The shastras state clearly that an aggressor — an atatayee — may be killed without incurring sin. Arjuna knows this rule. But he cannot bring himself to apply it here, because these aggressors are also his own flesh and blood. It is like a family where someone has gone down a wrong path. Punishing them may be just, but it tears the heart apart.
Arjuna's conflict here is between dharma and love. What is right and what he can bring himself to do are no longer the same thing.