But the most important feature is healing for the victims, the partial return of justice. When someone is murdered or raped (let's not cloud the discussion with morally ambiguous crimes like drugs), the victims and their families have the fabric of their lives completely torn up; they experience immense pain and suffering. Yes, I'm going for pathos, and that's on purpose, pathos is central to the argument. The knowledge that the perpetrator has pain inflicted on him is an important factor in stitching their lives back together. I'd love for a proponent of the "rational" argument to sit down across from a mother whose daughter has been raped and explain that her feelings are irrational.
Yes, this is an irrational argument, but humans are irrational (the rape itself was probably a rather irrational act) - like it or not, that's a fact of how humans work. An order of society that ignores this fact is bound to fail.
There should be strong preventive measures in place, the best policy is the one where the crime isn't committed in the first place. Education and solid ways out of poverty are important factors here. Avoiding recidivism is also important. But once the crime is committed (which is the theme here), a narrow focus on rehabilitation is blind to the "red meat" of the issue.