“FIFTY SHADES OF GREY,” the quasi-pornographic bestseller that is doing for sado-masochism and leather crops what Harry Potter did for British boarding schools and broomsticks, is a publishing sensation — a supernova in the zeitgeist and a cultural lightning rod. It’s also atrociously written — proof positive that execrable prose is no bar to dominating the bestsellers list.

The book, by previously unknown British author Erika Leonard (better known by the pseudonym E.L. James), concerns the no-holds-barred sexual affair between a billionaire Adonis with a taste for bondage and beatings and the ingenue who loves him and takes pleasure in accommodating his tastes. Having appeared on the cover of Newsweek in April, the book is the subject of lively debate about whether it represents a milestone in the debasement of Western culture; harmless low-brow entertainment; or a tectonic shift in post-feminist fantasies.

Regardless, what’s clear is that millions of people, especially women, want to read it. So should libraries stock it? Most, citing a tsunami of popular demand, have decided the answer is yes. A few, including the library system in Harford County, Md., north of Baltimore, have declined. “It’s clear that we don’t buy pornography for the library,” said the director, Mary Hastler.

Her decision has brought her a good deal of abuse, which is unfortunate. Like librarians in Wisconsin, Florida and Georgia, she was doing her best to adhere to established criteria for upholding community standards.

The trouble is that community standards — and good luck defining them — are no longer set by librarians or library boards any more than they’re set by schools and school boards. In a wired world, they’re set by communities themselves. Ms. Hast­ler’s view of what community standards should be isn’t necessarily illegitimate. But the community itself happens to disagree, and it pays the bills.

Public libraries once played the role of gatekeeper, but the gate is gone. Libraries exist — and thank heavens they do — to serve the public. “Fifty Shades of Grey,” the first book in a paperback trilogy from Vintage Books, has sold more than 10 million copies, and individual local library systems across the country have reported thousands of requests for it. The public has spoken; libraries probably ought to listen.