This reads like a wingnut parody of degenerate France and degenerate Hollywood engaging in an orgy of amoral pomposity. (As a lawyer I confess ignorance regarding the principle of immunity from legal process for film festival attendees).
I can only hope that most of the signatories to this kind of thing aren’t actually familiar with the facts of the case. Of course that sort of selective blindness is a huge problem of its own.
As djw notes in a thread below, the worst part of minimizing Polanski’s crimes is that almost all the arguments used to do so are classic rape culture tropes. (Consider the central claim of this petition, which is that Polanski was arrested on a “morals” charge, as if it were obvious that it’s perfectly possible for a 44-year-old man to have genuinely consensual sex with a 13-year-old girl, let alone one he had first drugged up, and who has always insisted that she was forcibly raped).