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.
The prison sentence is the punishment for the crime. After people are let out of prison they should be reintegrated into society.