I hope I am not stirring up too much controversy by discussing this subject that came up as an aside in another thread.
I agree it seems unfair, on the surface, to offer inmates subsidized education without giving all law-abiding citizens on the outside similar benefits. However, this is not such a simplistic black-and-white issue. Our prisons now mainly provide punishment and very little rehabilitation. Criminals go there to rot and become hardened and bitter for a few years and then are released in worse shape than when they went it. Without any improvement in their personal situation, many end up returning to crime, hurt more people, and get back to prison again and again.
This revolving door is very costly to society both in terms of people getting victimized by the repeat criminals and the high costs of maintaining our LE and prison system. Yes, it sounds unfair, but in the long run, if we can help inmates become wage-earners, it saves taxpayers' money, reduces crime, and makes our society safer. It is in our own self-interest to do so.