कुलक्षये प्रणश्यन्ति कुलधर्माः सनातनाः। धर्मे नष्टे कुलं कृत्स्नमधर्मोऽभिभवत्युत॥
kulakshaye pranashyanti kuladharmah sanatanah dharme nashte kulam kritsnam adharmo'bhibhavaty uta
Translation
With the destruction of the dynasty, the eternal family traditions perish. When traditions are lost, the whole family is overcome by irreligion.
Commentary
Arjuna fears the social consequences of war — the destruction of family lineages will lead to loss of traditions, which will lead to moral decline. This is a sociological argument against war.