i just saw the documentary on this, and it makes it feel like a very very complicated situation.
judging from what polanski was saying about his sexual tastes (he admitted repeatedly that he is just attracted to young, and young-looking girls, and that the criminalization of this doesn't exist in france), he seemed to be naive about the laws in place in america. i think that, no matter how fucked up it seems to most people here, this is a culture difference in effect, especially in that era.
plus, if you watch the doc, you'll see how incredibly ridiculous and grandstanding the judge on the case was. he operated from an egotistical point of view in almost every respect, and polanski would have served every bit of sentence and this would be over with any other judge. but this one made severely erratic decisions throughout the case, the most erratic being the decision to further punish him after agreeing to limit the punishment to the original six weeks because of a harmless photo that got circulated after his term was served.