Even if you cannot see the other person, there is no need for us to close our eyes.
Arjuna believes that Duryodhana and others have had their minds clouded by greed, making them unable to see the evil of destroying a clan or the sin of betraying friends. They have lost the ability to distinguish between good and bad, and they do not understand what kind of disaster their actions will bring.
However, Arjuna and his brothers are different. They clearly see the evil that will be brought about by the destruction of their clan. It is not a reason for them to fall into the same sin simply because the other party does not understand. Rather, those who can see it may have a responsibility to withdraw from it. Arjuna's argument shifts the focus from the ignorance of the other party to the choices made by themselves.
Japanese Translation from the Gita Press Edition - Chapter 1, Verses 38-39: "If your mind is not clouded by greed..."
Those who see with eyes clouded by greed, Do not perceive the faults of their own family, and also commit sins against friends. || 38 ||
How can we avoid sin? O wise one, those who see the faults of their own family will understand. || 39 ||
Vocabulary
"yadi api" is "even if".
ete means "these people."
"na pasyanti" means "does not see" or "does not understand."
lobhopahatacetasaḥ means,
"Those whose minds have been corrupted by greed."
kulakṣayakṛtam doṣam means,
"An evil that arises from the destruction of a lineage."
mitradrohe pātakam is,
"a sin associated with betraying a friend."
katham na jñeyam asmābhiḥ means,
"How can we not know?" or "Why should we not think?".
It is often translated as, "How can we possibly know?" or "Why shouldn't we think about it?".
The phrase katham na jñeyam asmābhiḥ is a rhetorical question. It implies that the speaker believes that there is no way to know something without thinking about it.
pāpāt asmāt nivartitum is,
"to retreat from this sin."
"prapaśyadbhiḥ" means "by those who are clearly seeing."
"Janardana" is a name used to address Krishna.
Translation
"Even if they, whose minds are clouded by greed, do not see the evil of destroying a clan, nor do they recognize the sin of betraying a friend, Janardana, we who clearly see the sin that arises from the destruction of a clan, why should we not consider withdrawing from this sin?"
Annotative Translation
Here, what Arjuna is about to say is: the following thing.
The actions of Duryodhana and his companions are, without a doubt, highly reprehensible.
However, for them, it was not an unnatural thing.
Because, their excessive greed completely destroyed their ability to distinguish between good and evil.
Therefore, they were unable to see the great evil and misfortune that would inevitably result from the destruction of all members of their clan.
Also, they did not understand how terrible a sin it is to regard relatives and friends as enemies, and to fight in order to kill each other.
However, Arjuna and his brothers were not blinded by greed.
They were able to clearly see what kind of evil and misfortune arise from the destruction of a family and clan.
Then, even though you know it, with your eyes wide open, why should you commit such an enormous sin?
They should consider the evil nature of that action, and withdraw from the fight.