निहत्य धार्तराष्ट्रान्नः का प्रीतिः स्याज्जनार्दन।पापमेवाश्रयेदस्मान्हत्वैतानाततायिनः॥
nihatya dhārtarāṣṭrān naḥ kā prītiḥ syāj janārdanapāpam evāśrayed asmān hatvaitān ātatāyinaḥ
Word by word
The verse says
What joy could there be for us, Krishna, in killing Dhritarashtra's sons? Killing these aggressors would only bring guilt upon us.
In plain words
Notice the word he uses for them: ātatāyinaḥ, aggressors.
That is a precise legal term. It means someone who has committed one of a short list of grave crimes — arson, poisoning, seizing another's land or wife. The old law codes are explicit that killing such a person is permitted and carries no sin.
Arjuna has picked exactly the word that undoes his own argument, and he uses it as though it supported him.
Where you've felt this · at work
In the middle of insisting you were treated unfairly, you use a word that quietly concedes the other side had a case. You hear it as you say it. You keep going, because stopping would mean dealing with it.
Going deeper
This is the first real crack, and it is a small one made of a single word.
The Kauravas fit the definition. They burned the Pandavas' house with them inside it, tried poison, seized the kingdom, and dragged Draupadi into the assembly hall. By the standards Arjuna himself was raised on, they are textbook ātatāyinaḥ, and the law is not ambiguous about them.
So his sentence, read closely, says: killing these people, whom it is lawful to kill, would bring us guilt. The two halves do not fit together, and he does not appear to notice.
This is what it looks like when a conclusion is fixed and the reasons are being fetched afterwards. Arjuna is not arguing his way to a position. He arrived at the position in verse 30, when the bow slipped, and he has been assembling justifications ever since. From here they get steadily less his own.