Sridhara Swami's Commentary
It may be argued to Arjuna that if he does not slay his enemies due to feeling compassion for them, then they out of greed for power they will surely slay him; therefore it would be better for him to slay them and enjoy sovereignty. This is answered in a verse and a half beginning with: I do not like etc. Even if they kill us I do not like to kill them even for attaining the sovereignty of all the three worlds much less for gaining only this earth.
The Vedic scriptures declare that those who commit the following six types of crimes being : arson, poisoning, assaulting with weapons, stealing ones wealth, usurping ones land or kidnapping one's wife are aggressors and Duryodhana and the Kauravas were definitely aggressors having committed all six offences against the Pandavas beginning with arson. The slaying of aggressors is justifiable and the Vedic scriptures state that one should slay an aggressor coming with the intention of committing a criminal act without hesitation and that the slayer of such an aggressor incurs no sin whatsoever. This is being answered by the verse and a half beginning with: sin alone etc. The text which states one should kill belongs to what is called an Artha Sastra which is a scripture dealing with the rules and laws regarding wealth. Artha Sastra is considered less authoritative than Dharma Sastra which are scriptures dealing with righteousness. Dharma Sastra is superior to Artha Sastra. As it is stated by the sage Yagnavalkya: when two scriptures differ the one whose conclusion is the most reasonable and most logical is to be considered superior. This is the understanding. Therefore by the slaying of preceptors etc. although they are aggressors, Arjuna is stating that sin shall be incurred because such slaying is unwarranted and unrighteous. There can be no happiness from this. This is being given by: How can we adopt this course of action?
Although Duryodhana and the Kauravas being deprived of all discrimination are determined to fight; why should we who are not deprived of discrimination become degraded as well by such sinfulness? We should resolve not to engage in this battle.
It may be argued that the action of slaying kinsman is common to both the Pandavas and the Kauravas; so even as the Kauravas adopting such a contingency are determined to fight; it is better for Arjuna to likewise engage himself in the battle, what is the value of despondency? This is being answered by these two verses.