No, that is not the purport of selfless killing. Selfless killing is killing for no personal gains. It is not even killing in self defence. In Arjuna's case, there is almost no choice to get merely the upperhand, but to exterminate the wicked.
Pandavas had spent 13 years of torture in the forest, even at a time when they were very powerful and could obtain the kingdom by brute force. They simply decided against it solely because Yudhistira had given a promise.
After their hiding period, the Kauravas were supposed to return their kingdom back. The promise was not kept. Pandavas send a message saying that they would be just satisifed with five villages instead. But the enemy was not willing to give five pin-heads of kingdom.
Thus, Pandavas are left landless, homeless and to wander in the forest. Even then, they sent Krishna as messenger to make peace. The attempt fails due to the arrogant attitude of Kauravas. The war is a last resort in which Arjuna has a moral right to kill everyone and take back his kingdom.
Even so, the great souled Arjuna cracks down and refuses to kill anyone for the sake of his pleasures and even volunteers to retire to the forest. Bhagavad Gita starts off from here. Arjuna is a great soul, who has had the wisdom to know that killing is wrong under any circumstance, for personal glory. Krishna would not teach any person less worthy than someone like Arjuna, to whom all the wealth and riches are nothing.
The Gita is merely a message for the world. Arjuna hardly needs the message himself, who has already known the limitations of the material pleasures. If all warriors were to get sentimental and even ascetic like, who will punish the criminals? Thus Krishna seeks to just sort a little bit of confusion in Arjuna. Rest of the stuff is for the world, not for Arjuna. He knows them all anyway.
