Taking jobs from Americans who need it.....forcing those displaced workers on unemployment..... and the good life.
There are not a finite or fixed number of jobs out there. The labor market is dynamic, constantly bending and stretching and adapting, and somebody having a job gives them income and enables them to consume (or pay off debt) they otherwise cannot. New workers do not just fill demand for work -- they create demand for it, as well.
Right now is not a great time to illustrate this, given we are likely in the middle of a historic contraction in the labor market (though not for "economic" reasons on their own), but roughly a quarter off all U.S. jobs turnover in a given year. That is, over a 12-month period, roughly 25% of workers will move on to another employment opportunity.
Your other reasons to oppose some sort of work-release -- would not generate much money, creates a huge flight risk, does he really deserve to be let out, etc. -- are stronger arguments, but the "They took our jobs!" one is not a sensible one here.