दोषैरेतैः कुलघ्नानां वर्णसङ्करकारकैः। उत्साद्यन्ते जातिधर्माः कुलधर्माश्च शाश्वताः ॥

doṣhair etaiḥ kula-ghnānāṁ varṇa-saṅkara-kārakaiḥ utsādyante jāti-dharmāḥ kula-dharmāśh cha śhāśhvatāḥ

By these caste-confusing misdeeds of the slayers of the family, the everlasting caste customs and family customs are abolished.

In plain words: Arjuna says that the wrongdoing of those who destroy a family wipes out the old customs of both caste and family.