Whether you think the Bible is the word of God or not, one thing is pretty clear: it relates some disturbing stories. Some of those stories can even be termed as sordid. Genesis 34 contains an account of moral degradation that is almost unrivaled (though the story contained in Genesis 38 comes close, and Judges 19 probably exceeds it) in terms of moral perfidy.
Genesis 34 relates the account of the sexual violation of Jacob's daughter Dinah, followed by the shocking overreaction by her brothers. In order to understand it properly, one might first note events in Genesis 23. That chapter tells of the reunion of Jacob and Esau.
In verse 14 of Genesis 23, Jacob refuses his brother's invitation to travel under guard. Jacob here is apparently putting his trust in God's protection rather than Esau's sword-bearing men. But Jacob, whose actions are frequently laced with deception (Genesis 25:29-33; 27:22-24; 31:20) tells Esau "So let my lord go ahead of his servant...until I come to my lord in Seir."
Jacob apparently had no intention of going to Seir (located southeast of Canaan) and instead settled near the city of Shechem in Canaan. In doing so, he delayed his return to Bethel, never did go to Seir, and made a decision that may have set the stage for the events of chapter 34.
Jacob, though considered a righteous man, made an decision similar to that of Lot, who also decided to locate near a city with inhabitants of questionable character (Genesis 13:12). His daughter Dinah then "went to visit the women of the land". While she is often criticized for doing this in religious commentary, it should be remembered that as a young woman, she would naturally seek companionship among female peers. She had no such peers among her family, and they were now encamped far from the land of Paddan-Aram, where her only other relatives lived. Indeed, God's direction that Abraham and his descendants were to live in the land of Canaan brought unique challenges to the patriarchs and their kin.
From this point, chapter 34 prsents a cascade of sin, culminating in a heinous crime by two of Jacob's sons, Simeon and Levi. His other sons later took spoil from the slaughtered Canaanites, so they too would bear responsibility for making Jacob "a stench" to the inhabitants of the land. (vs 27-30).
All parties in this account were to blame to varying degrees for what had transpired. Shechem violated a young woman. Though he tried to make amends, he certainly was deserving of punishment. The other people in Shechem were perhaps guilty of greed (vs 23). The sons of Jacob did worse - besides murder and pillage, they were guilty of deceit (vs13) as well as guilty of using the sacred ceremony of circumcision with wicked intent (vss 14-17). Jacob, after making the questionable decision to move close to a Canaanite city, seemed to defer to his sons rather than assert is patriarchal authority. It was his sons who proposed the circumcision agreement, and they agreed (as part of their ruse) that the family of Jacob should intermarry with the Canaanites (vs 16). Jacob should have stopped things right then and there instead of allowing his sons to make a proposal that even on the surface was against what Jacob perceived as the will of God. Was it not Jacob who went to Paddan-Aram to find a wife rather than seek one from among the Canaanites, as his brother Esau had done? (Gen 28:1, 2).
People who read this account are often quick to blame Dinah, but as I see it, there's a heavy burden of blame to be shared by those around her.