In the Times a couple days ago, the writer Robert Harris, who’s been working with Polanski on a film adaptation of his book The Ghost, wrote what strikes me as the sanest, most lucid piece of thinking about the Polanski matter I’ve yet seen.

The question Harris asks is one we’ve all been wondering: Why now?

I have worked several times with Mr. Polanski in Switzerland, where he owns a house in Gstaad. He travels back and forth from France a dozen times a year. If Mr. Polanski is such a physical danger and moral affront to civilized society that he must be locked up, even at the age of 76, why was he not picked up earlier, when he was 66, or 56 — or even 46? It would not have been hard to grab him at his home: his name is on the doorbell.

He notes that the prosecutor in the case, Stephen Cooley, has released a timeline purporting to show a sustained effort over decades to arrest Polanski, and rightly points out that the timeline demonstrates exactly the opposite: Efforts to arrest the filmmaker over the decades have been haphazard and halfhearted.

So what changed? Ironically, it was the release of the documentary Roman Polanski: Wanted and Desired.

[Polanski] thought he could settle the matter at last, and his subsequent, vigorous legal attempts to have the case against him closed — supported, remarkably, by his victim, Samantha Geimer, the one person who comes out of this affair with her dignity enhanced — clearly infuriated Mr. Cooley. Legal authorities the world over loathe being publicly criticized. After the arrest was announced, Mr. Cooley declared that Mr. Polanski “has been trying to get it resolved on his terms, but it’s going to be on the terms of the Los Angeles County justice system.”

Polanski, Harris argues, became overconfident—both in the rightness of his cause and in the safety of Switzerland.

A Los Angeles Times article about Cooley’s third campaign for D.A.—breaking a promise Cooley had made that he would resign after two terms—suggests another reason.

…he came under attack for not moving more aggressively against Los Angeles Roman Catholic Archdiocese leaders for their role in protecting accused pedophile priests. He has also earned a reputation for frank talk — sometimes too frank. …Speaking publicly to an audience of attorneys, he used the F-word, saying he was doing things his own way and if the association didn’t like it, ” . . . them.”

And then, of course, you have Switzerland sacrificing Polanski in order to ease pressure on its banking system from international regulators.

So that is why now. But the question Harris concludes with is, Why at all?

I make no apology for feeling desperately sorry for him. The almost pornographic relish with which his critics are retelling the lurid details of the assault (strange behavior, one might think, for those who profess concern for the victim) makes it hard to consider the case rationally. Of course what happened cannot be excused, either legally or ethically.

But Ms. Geimer wants it dropped, to shield her family from distress, and Mr. Polanski’s own young children, to whom he is a doting father, want him home. He is no threat to the public. The original judicial procedure was undeniably murky. So cui bono, as the Romans used to say — who benefits?

Some would say society benefits as we show our commitment to cracking down on rape. I’m not so sure. Just look at the increasing polarization and nastiness of the comments on the blog below; or look at this hysterical response to Harris on the Huffington Post. (Sample: “Why now? …Why the fuck not?”)

The truth is, the status quo of Polanski’s exile from the US, unsatisfying to all parties though it was, was probably the way things should have stayed. Mr. Polanski would have died with a dark stain on his biography that was never resolved and, by many, never forgiven. That seems to me heavy punishment. Some might say not heavy enough, some might say too much. I reside in the uncomfortable middle. We Americans like to be literal in our punishment; in our justice system as in our movies, we want to see the blood. I feel that a permanent weight on a man’s soul is a profound burden, and you don’t have to be behind bars to feel it.

But we’re not going to learn or demonstrate anything new in pursuing this bound-to-be divisive matter. After all, the facts of what Polanski did are not in dispute, and 98% of the population appropriately disapproves, and the other 2% isn’t about to change its mind. This prosecution will degenerate into a hysterical circus in which reasoned discussion is overwhelmed by tabloids and extremists.

We’re merely going to demonstrate again— as we did during the first Polanski trial—the danger of pricking a lawman’s ego. Did we learn nothing from Ken Starr?