Bhagavad Gita 1-36

pApamEvAshrayEdasmaan hatvaitAnAtatAyinaHa

tasmAnnArhA vayaM haMtuM dhArtarAShTrAn sa-baMdhavAn

swajanaM hi kathaM hatvA sukhinaHa syAma mAdhava || 36 ||

"We gain only sin if we kill such invaders. So killing sons of Dhritaraashtra is not suitable for us. Oh Madhava; how can we be happy after killing our own relatives and friends?"                                  

Arjuna says killing such invaders (felons) will not do any good to us. It will only add to our sins. So killing sons of Dhritaraashtra is not suitable for us. This seems to be an interesting argument. On one side Arjuna says they are invaders but on the other side he says killing them is not a good idea. The author wants to highlight how weak this argument was. Arjuna in an attempt to make his view of not participating in the war goes on giving multiple reasons. When one is not convinced about one's own idea but has to convince others about the same one will choose a main reason and substantiate with multiple other reasons which may or may not be valid. This is what Arjuna is trying to do. How can killing the invaders be disgraceful? So Arjuna continues and says that he cannot be happy after killing his own relatives and friends. So the main reason is killing being at war with his relatives and friends. It means to say that if the opposition were unrelated to him he did not have a problem to fight them. He was not bothered about the human loss if they were not related to him.