Below are excerpts from Rav Shimshon Rafael Hirsch and his explanation as to why they reacted as they did. Note that Yaakov objected to this and did not accept their justification of "hora'as shah". See the full explanation in the 5 volume Hirsch Chumash.
Rav Hirsch says on 34:25
Now the blameworthy part begins, which we need in no wise excuse. Had they killed Shechem and Chamor there would be scarcely anything to say against it.
Their one answer in "hakezona" gives their whole motive. The lord would never have allowed himself to act as he did were it not a question of a foreign, friendless forsaken Jew-girl.
They wanted to make themselves so feared that nobody would attempt anything similar.
It is only the means they took and their going much too far in their use of them that was blameworthy.
Also, the fact that the entire city was ready to go along with the pretense of circumcision in order to con the Jews into becoming theirs meant that everyone was ready to be complicit.
Rav Sorotzkin in Oznayim Latorah takes a different viewpoint. He says that rather than an individual crime, which would require a bais din and restrict the punishment to individuals, this was actually a declaration of war. That is the fact that the Shechem, the eponymous prince of the city, kidnapped Dinah, raped her, and then hypocritically "offered" an bride price for her amounted to a declaration of war upon the people of "Yisrael". He notes that part of the response is "such is not done in Yisrael". That is, the term is not being used to reference Yaakov himself, but as a reference to the group as a whole.
Rav Sorotzkin also notes that they discovered (either from their servants or from ruach hakodesh) that the people of Shechem planned to "take their daughters" (whether willing or not), give them "our daughters" (if we feel like fooling them), and make everything of theirs ours. The people of Shechem knew that eventually, the Bani Yisrael would object and have to be killed in order for the full transfer of property to take effect. They were all willing to pretend to "convert" in order to trick the Bnai Yisrael into trusting them and enabling them to defeat the "interlopers". Since the Bnai Yisrael knew this and that the war had already started, they attacked first after having weakened the enemy.
Note the connection between the lack of bargaining here and the lack of bargaining that Lavan did (as Rav Sorotzkin explained there). This means that when someone never intends to keep a bargain, he will immediately agree to whatever is suggested as a price. Since he does not intend to keep it in the first place, he does not care what he is agreeing to.
Rabbi Yakov Haber says that the expected (or likely) scenario would have been that enough of the people would refuse to be circumcized to allow Chamor to "save face" and return Dinah in a "diplomatically correct" manner (while perhaps punishing Shechem in some way). Even if they agreed (as they did), a rescue mission could then have been mounted. It was only Shimon and Levi that went all the way and killed everyone (which is why they were chastised).
When Shimon and Levi seized the opportunity to exact vengeance from the entire city, somethin Yaakov Avinu did not anticipate, he censured them for killing those not directly involved in the attack and kipnapping of Dinah.
By Rabbi Mordechai Kamenetzky
The question is simple: Why ask the people of Shechem to circumcise?
If Yaakov's children wanted to attack them, why go through a process
of converting them? They should have asked them to fast for three
days. That would have made them even weaker. They could have asked
them to hand over all their weapons. Why ask them to do an act is so
On September 30, 2000, the word intafada was almost unknown to the
average American. And then the riots began. On one of the first days
of what has now been over three years of unceasing violence, against
innocent Israelis, The New York Times, Associated Press and other
major media outlets published a photo of a young man who looked
terrified, bloodied and battered. There was an Israeli soldier in the
background brandishing a billy-club. The caption in everyone of the
papers that carried the photo identified the teen as an innocent
Palestinian victim of the riots -- with the clear implication that the
Israeli soldier was the one who beat him. The world was in shock and
outrage at the sight of the poor teen, blood oozing from his temple
crouching beneath the club-wielding Israeli policeman. Letters of
protest and sympathy poured in form the genteel readers of the gentile
The victim's true identity was soon revealed. Dr. Aaron Grossman wrote
the NY Times that the picture of the Israeli soldier and the
Palestinian on the Temple Mount was indeed not a Palestinian. The
battered boy was actually his son, Tuvia Grossman, a Yeshiva student
from Chicago. He, and two of his friends, were pulled from their
taxicab by a mob of Palestinian Arabs, and were severely beaten and
stabbed. The Israeli soldier wielding the club was actually attempting
to protect Tuvia from the vicious mob.
All of a sudden the outrage ceased, the brutal attack was almost
ignored and a correction buried somewhere deep amongst "all the news
that is fit to print" re-identified Tuvia Grossman as "an American
student in Israel." It hardly mentioned that he was an innocent Jew
who was nearly lynched by Arabs. This blatant hypocrisy in news
coverage incidentally help launch a media watchdog named Honest
Rav Yonasan Eibeschitz, zt"l, explains that Yaakov's children knew
something that was as relevant in Biblical times as it is in today's
"New York" times. Yaakov's sons knew the secret of society. Have them
circumcised. Make them Jews. Then you can do whatever you want with
them and no one will say a word. You can wipe out an entire city -- as
long as it is not a gentile city. If Shechem had remained a gentile
city had the people not circumcised according the laws of Avraham then
Yaakov's children would have been condemned by the entire world. But
Yaakov's children knew better. They made sure that the Shechemites,
went through a Jewish circumcision. Shechem now was a Jewish city; and
when a Jewish city is destroyed, the story becomes as irrelevant as an
American student attacked by a Palestinian mob in Yerushalayim!
Unfortunately it is that simple and that old.