Adam Clarke on Genesis 34:14

That were a reproach unto us - Because the uncircumcised were not in the covenant of God; and to have given an heiress of the promise to one who had no kind of right to its spiritual blessings, from whom might spring children who would naturally walk in the way of their father would have been absurd, reproachful and wicked. Thus far they were perfectly right; but to make this holy principle a cloak for their deceitful and murderous purposes, was the full sum of all wickedness