There are a lot of very funny scenes, including Luke's initial assault on the parking meters, the lengthy sequence where a luscious blond exhibitionist lathers up her car as the inmates look on, and of course the scenes described above where Luke wins over the other inmates. Not all the guards are bad guys. Just doin' my job. You gotta appreciate that. But as portrayed in the movie, we understand the guard is himself constrained.
Captain is also a mixed character.
We get the sense that he really thinks that he is doing what is best for the prisoners. Only Godfrey is pure, mute malevolence. And among the prisoners, several dissent from the prevailing opinion about Luke. This is not a straight-forward call for prison reform by any stretch, and indeed, the movie barely comments on the severity of Luke's sentence for what seems like a petty crime. In short, although ostensibly the movie is about the triumph of a unique spirit, it has a much more complicated, darker, and more ambiguous subtext.