It's in everyone's interest for criminals to learn from their mistakes and become functioning members of society. How could they conceivably do so if they're eternally denied education, employment, or even shelter on the basis of their past deeds?

NB, this is argument applies even if you're trying to make the argument to a very pro-law-enforcement person who accepts the premises that only guilty people need to worry about the police and that the laws are perfect so everything that is a crime ought to be one.