Sridhara Swami's Commentary
It may be argued: That without slaying them it would not be possible for Arjuna to even maintain his own body. So Arjuna is responding that without slaying his superiors like Bhishma and Drona which bars one from the heavenly kingdoms it would be better to live in this world even on food obtained by begging without causing the death of anyone. Otherwise misery will be the result not only in the next life but even in the present Arjuna was stating he would be experiencing the miseries of hellish existence. This is verified by Arjuna saying that by slaying elders and superiors even in the present life all the spoils he would be enjoying would be tainted with their blood.
Another interpretation is that the word arthakaman may be also taken as qualifying the elders and superiors. These elders being consumed by greed of wealth are not likely to refrain from war. Therefore they will have to be slain. Bhishma for an example spoke to King Yudhisthira saying: Man is a slave to wealth but wealth is the slave of no man, this is the truth. O Emperor I am bound to the Kauravas by the acceptance of wealth.