On the wrong side?

I realized just this year, perhaps later than everyone else, that I have been misunderstanding the entire* story in Genesis about the massacre at Shechem by Shimeon and Levi occasioned by the rape** of Dinah. I have always taken it as obvious that Shimeon and Levi did the wrong thing - that Jacob scolded them, and that their answer ("Is our sister to be treated like a harlot?") is self-righteous indignation. For the first time, I realize that the Chumash* does not disapprove of the actions of Shimeon and Levi. The reason Jacob says nothing after Shimeon and Levi's response is that he has lost the argument. The reason the Chumash does not disapprove is that God is on the side, here, of those who massacre the unclean.

*Putting aside for a moment the multi-authored nature of the Chumash, which I think is evident.
**If you think "rape" is the right translation - open to question.