How do we deal with sin?

Why on earth is Genesis chapter 34 in the Bible? It's just one horrible act after another, with no (it seems) redeeming features at all. Jacob's daughter Dinah is raped by one of the Shechem locals, and then his sons kill all the men in the village in a deceitful, vicious act of revenge. And that's it. But, it's chapters like this that demonstrate that the Bible doesn't gloss over the reality of sin in the world and the capacity that exists for evil. The Bible is honest and it is hopeful, showing that there is a better way to deal with sin than taking matters into our own hands.