It isn't, but rape is one of those under-reported, under-prosecuted crimes that horrifies everyone to the core, and while most people have a visceral and emotional reaction to it (which is fine) most will not take it to any form of mob justice and have faith that eventually the legal system will evolve into doing the right thing every time.
But this kind of emotional reaction (to pedophilia - I agree that rapes are under-prosecuted) has
already pervaded courtrooms and the legal systems. It's not litteral lynching I'm afraid of, it's that justice isn't served well with the kind of hysterical public and media pressure these cases bring. Along with glaring instances of miscarriages of justice. Just being accused of such a crime is a sentence in itself. It shouldn't be so.
The reaction to Polanski is multiplied by several factors, including the fact he's wealthy and privileged and surrounded by a phalanx of wealthy and privileged allies. This shatters the aforementioned faith and people are lashing out because they feel helpless in the face of this injustice.
Well this is indeed a cause for outrage. And what happened in France is terryfying evidence of just that: the realization that the US justice would dare and try to reach a member of the aristorcracy without any regard to the privileges such members usually expect from local justice.
Polanski's conduct and position in the world is a big ugly lump of things representative of the worst in humanity and society. That is the most rational thing I can think to say about him and I can't really fault human beings for not completely divorcing their emotional response from what they want to say about him in a public forum. I see little gained from asking those voices to calm down and hope for the best.
Rape is a horrible crime but in this day and age I hardly think that Polanski's conduct and/or his position has been or is in any way representative of the worst in humanity and society.
And I see little gain in brandishing pitchforks and wish for the worst either. And allthough I'm not advocating silencing anyone, adequate response does requires to divorce from emotional response. That's why justice isn't and shouldn't administered by victims, or by angry neighbours for that matter.