Or HaChaim on Genesis 34:31/אור החיים על בראשית ל״ד:ל״א

1 ויאמרו הכזונה יעשה את אחותינו, They said: "Should we have let him treat our sister like a harlot?" We need to understand how such a reply could have had any bearing on Jacob's concern for the survival of his family in a possible confrontation with the other Emorites in the region? After all, Jewish law provides that if the surrender of a specific individual is demanded by enemy forces as a condition to save the lives of the remaining prisoners, then such an individual must be surrendered (Jerusalem Talmud Terumah chapter eight) in order to save the lives of all the people who this individual is part of. There is no requirement for all the people to become martyrs even if the alternative is the commission of a serious crime of ערוה, incest or other sexual crime. Seeing that this is so before such a sin has been committed, it is all the more so after the crime has already been committed and cannot be reversed!

2Perhaps the brothers merely wanted to calm the fears of their father saying that a confrontation with the Emorites would be a real danger only if they had killed the people of Shechem without an adequate reason. Under the circumstances, when kidnapping and rape had been committed, they did not think the other Emorites would raise much of a fuss. Legally speaking, of course, Shechem had not been guilty of harlotry seeing Dinah had been unattached at the time. Categories of sexual intercourse forbidden to the Gentiles include only homosexuality, adultery, bestiality, and intercourse with the sister of the same mother.

3It is also possible that the brothers considered their action as one that would serve notice on the Emorites not to take liberties with their family. Having seen what happened to an individual who used violence against a member of Jacob's family, the Emorites would take this to heart and be forewarned of the consequences of such deeds in the future.