I admit I've only skimmed the article and the comments on HN, but I don't think that either have mentioned the CCPOA (California Correctional Peace Officers Association). It's basically a union of prison guards who are heavily pro-incarceration. The quick version is that stricter laws produce more prisoners which leads to more money for prison guards and their organization. The story is better told here:
http://ordinary-gentlemen.com/blog/2011/06/05/the-role-of-th...
The phrase "prison-industrial complex" leads to some interesting reading, as well.