I also agree that once the sentence has been served, people should not be punished any further, except where the occupation requires a clean record. e.g. I would be OK with pharmacies requiring no arrest for drugs etc. as a condition for employment, or drivers without DWI convictions etc.
I guess my point is: its not a purely economic decision. Sure you're losing tax revenue, but that's because you're:
1) Protecting society from a person who has demonstrates some lack of understanding/acceptance of its rules.
2) Cause significant discomfort/pain to the perpetrator of the crime so that they realize the consequences of breaking the law and hopefully never do it again.