Arjuna continues the chain of consequences. O Krishna, he says, when adharma rises, the women of the family are led astray. And when women lose their way, O Varshneya, varna-sankara arises — the social order breaks down completely.
In Arjuna's world, the stability of the family and the continuity of tradition rested on a well-ordered household. When the men are killed in war, families are left unprotected and unguided. The structure that held everything together weakens and eventually collapses.
Put simply, Arjuna is saying that war does not only destroy people on the battlefield. It destroys homes. When the protectors are gone, the household itself falls apart. The consequences of war reach far beyond the place where it is fought.