In my opinion, it was despicable what he did. and deserves some legal punishment.
But it was more of a jailbait scenario, rather than the kind of forcible kidnap/rape of a virginal pre-pubescent child that really deserves much more extreme punishment.
There are gradations, and extenuating or mitigating matters when it comes to human sexuality, that would make each case relatively more or less of an affront.
A large percentage of Americans have sex before the age of consent (average age is 17).
Yuck
He drugged her, and raped her. It was legally rape. It was technically rape. It was rape rape. No mitigating circumstances. No excuses. He needs to serve hard time for raping a child.
In addition to that, the crime was not only against her, but against the People of California. They have weighed in on this through their elected representatives and legal system.
No one would be showing any consideration to this man if he was a 40 year old semi-toothless meth head living in a double wide who raped his 14 year old niece -- with or without her consent. IIRC her own mother acted as a procurer in this case, and she also should have faced some consequences.
Polanski (and the people who support him) believe that they get to live by a different set of laws than the ones society has created for all of us -- with our own consent.