Bhagavad Gita

ನಿಹತ್ಯ ಧಾರ್ತರಾಷ್ಟ್ರಾನ್ ನಃ ಕಾ ಪ್ರೀತಿಃ ಸ್ಯಾಜ್ಜನಾರ್ದನ ।
ಪಾಪಮೇವಾsಶ್ರಯೇದಸ್ಮಾನ್ ಹತ್ವೈತಾನಾತತಾಯಿನಃ ॥೩೬॥
nihatya dhārtarāṣṭrān naḥ kā prītiḥ syājjanārdana |
pāpamevāsśrayedasmān hatvaitānātatāyinaḥ ||36||

Sloka 1:36
Gist of the sloka:
By killing Dhitrarastra what will we gain Janardhana? We will in fact get sin, if we end up killing these people who are destroying the clan [parricide].
Arjuna is indicating that in case Dhitrarastra dies, then it would remain on their consciousness throughout their life affecting them with sorrow. Destroying the clan would only mean increase of sins and has no other benefit.
Arjuna uses the word “atathayi” to describe his cousins. The word means one who has lit fire to cause destruction to others property/life, one who has put poison in other’s food, one who has illegally obtained/occupied another’s property, one who has attacked another’s women etc.,
The dharma says such people who are “atathayi” needs to be killed wherever and whenever they are found. Preferably by the kshatriyas/rulers to ensure continuation of dharma.
Duryodhana, had qualified himself to be a “atathayi” in all criteria. He had lit the fire to house where Pandavas were staying. He had occupied the Kingdom which did not belong neither to him or to his father. He had poisoned Bheema. He had tried to disrobe his own sister-in-law Draupadi and that too in open court in front of his family elders.
Even after knowing all the above deeds of Duryodhana, Arjuna feels longing for his relations making him forget his primary duty to enforce dharma.
Arjuna is calling Lord Krishna as Janardhana. Which means one who destroys evil people and at the same time provides glorious death to his devotees who can then reach mukthi.
Arjuna is implying that being the Lord who gives mukthi to deserving; why do you insist on the war which only increases our sins and due to sins makes us continue to be born on earth again and again. Also, war is fought on basis of anger and desire, both of which is barrier to mukthi.