What's so bad about chametz?

From my Chayyei Yeshua article on 1 Corinthians 5:6-8 in this weeks edition of The Set Table:

Why the severe punishment for eating chametz? One possible reason is that what happens to the person after eating--expulsion from the community--is what should have happened to the chametz before it was eaten. In light of this connection, it shouldn't surprise us that Paul's exhortation to the Corinthians about ridding themselves of chametz comes in the context of instructing the community about putting a particular member out of their fellowship.

This may seem extreme to us, and so it is appropriate for us to ask the question: is such a judgment necessary? . . .