Fine, argues Arjuna : the steady-minded man is superior, because his mind thinks clearly. If mind, reason, thought, knowledge are so precious, why not stick to contemplation, which is pure, instead of recommending action, which is physical, impure ? Why say : 'Fight' ?Why not just : 'Think' ?
Krishna's answer is the key shloka 35 of Canto III : 'shreyam-svadharma' (one's own dharma is the best). At any given time a human being stands at the crossroads of four dharmas : sva-dharma (me-ness, self-preservations), kula-dharma ( family duties; geneological roots); yuga dharma (the spirit of the age, the nexus of the epoch; say Marxism, capitalism, Freudianism, feminism - in the twentieth century), and sanatana-dharma (the eternal values that mankind cannot change but which persuade mankind to change itself into, hopefully, a better, nobler, more 'human' species).
Arjuna is caught in a conflict of four dharmas. He thinks his sva-dharma is to lay down arms; his family Kshatriya dharma advises him to do battle; the dharma of the Dvapar-Yuga demands taking sides in the doomsday clash; and the sanatana dharma states that all life is sacred and the atman cannot perish.
Which dharma should he choose ? Only the naive, facile and overzealous will say that the sanatana dharma is always the best. Krishna's advice seems to be : Remember the heirarchy : lowest is the flesh; then come the senses; then the mind; the intellect; the atman. Steady yourself with your Self (samstabhi-atmanam-atmana) -- and choose. That is your dharma -- that is your choice.