Clearly the text was purposefully designed... The question is what the story is trying to teach. Is it merely history, or a parable? If the latter, what does it mean?

Rabbi Hoffman interpreted it as teaching that intermarriage is dangerous. He stated that, in the brothers' position, he might have felt justified taking the same actions, and I don't think that speaks well of him as a moral leader.

Now, it is possible that that is what the text intends to teach. If so, then it is a lesson of the Torah I can never agree with. Of course, it wouldn't be the only one...

I never consider revenge to be a valid justification for something immoral, and while I can see situations in which killing is necessary (even if it means some innocent people might die), I can't think of any situation in which such cruel deception could be justified.