There should have been some prosecution: not of the film maker, but on those who abused their power to harass people to the point of suicide.
Additionally, selective enforcement is primarily a tool of corruption. The law is supposed to apply to everyone. If it doesn't, then those who enforce it get to selectively choose to not enforce it against themselves and only enforce it against their enemies. And, as we've said, the government has very disproportionate power against its citizens, so to give prosecutors, police, or other enforcers of the law very broad, rarely used precedents is extremely dangerous.
A defense attorney who has proof that their client is 100% guilty must still defend their client to the best of their ability. A prosecutor who believes that the accused is innocent is ethically required to dismiss the case. (Obviously, this doesn't always happen, but it's supposed to.)
Add to that the costs of defending a court case, and the prosecutor has more-or-less complete power - they can financially ruin someone at will, just (as in this case) by deciding to enforce an obscure law that the defendant didn't even know about.
So making the prosecutors adverserial to the citizens, while giving them absolute power to destroy anyone they don't like, is a recipe for corruption.
The prosecutor took measures to avoid normalizing what he and the community saw as deviant behaviors. That's one of the key purposes of law: it allows society to express its condemnation of certain conduct.
However we can't formally accept that as a society without kicking out one of the main pillars supporting the justice system. If we expect and accept that the justice system to produce unfair outcomes it becomes challenging to justify having court appearances. We could get unfair outcomes much more efficiently by just letting the police and DA arrest whoever with regular internal purges against corruption.
Those laws should never have been used, and if the community wanted to dissuade future productions, they should have passed laws at the city, county, or state level that allows for the proper checks and balances.
I'd argue that there's a qualitative difference between selective enforcement that involves informal standards that evolve over time (e.g. police ignoring anyone who breaks the speed limit by less than 10MPH) and selective enforcement that involves a law that hasn't been enforced for centuries being pulled out of retirement and aimed at a single individual.