Under extreme duress from conservative news media (outlets such as NewsBusters, Breitbart.com, National Review and the Weekly Standard and bloggers including Michelle Malkin and Mollie Hemingway who have been on the case for a couple of years now) and with an added push from CNN’s Jake Tapper and Democratic journalist Kirsten Powers, the mainstream media began Friday to cover the horrific trial of abortion doctor Kermit Gosnell. Only then did media critics, who hadn’t noticed the MSM not covering the story, begin covering the media’s delinquency.

Why in the world did it take so long? It is not as if the story wouldn’t have drawn readers and viewers. The mainstream media would have had a sensational trial to cover. Gosnell’s butchery would have kept readers and viewers transfixed. And late-term abortion is clearly a matter of public interest. Moreover, the mainstream press extensively covers restrictions on abortion facilities — such as The Post did Friday on its homepage.

The only logical conclusion for the absence of coverage is the obvious one: the mainstream media’s overwhelming bias in favor of the pro-choice position. The Gosnell story is the pro-choice movement’s worst nightmare.

Planned Parenthood tweeted Friday that the Gosnell clinic was “appalling.” One has to ask why — since that organization fully supports every abortion, every time, for any reason — they felt squeamish about “infant beheadings. Severed baby feet in jars. A child screaming after it was delivered alive during an abortion procedure.” In Planned Parenthood’s book, this is all fetus elimination and fetuses are unworthy of legal protection. In the Gosnell trial, the horror of their extremism becomes painfully clear. We are horrified because of the humanity of the baby victims, whom pro-choice activists insist are “fetuses.”

The Gosnell case is also a vivid example as to why states do need to regulate abortion clinics, a move usually interpreted by media elites as just another element of the “war on women.”

As Megan McArdle wrote: “[T]his has disturbing implications for late-term abortions. It suggests that sometimes, those fetuses are delivered alive. Worse, it hints at what we might be doing inside the womb to ensure that the other ones aren’t.”

The mainstream media’s blindness toward stories that disadvantage the left is hardly new. The MSM have a track record of avoiding for as long as possible (excuse me, exercising “journalistic judgment”) stories like President Obama’s relationship with the Rev. Jeremiah Wright, Operation Fast and Furious and the attack in Benghazi — all of which, wouldn’t you know it, are bad for the left. Virtually no information damaging to Chuck Hagel, to cite another example, was uncovered outside conservative media.There was little interest outside conservative media in the record and rhetoric of the man who would head the Pentagon at a time of great international turmoil. The controversies over administration personnel from Chas Freeman to Van Jones again were covered almost purely by conservative media, and sometimes the editorial pages of mainstream outlets, eventually forcing grudging news coverage of legitimate stories.

And on abortion specifically, conservative outlets, columnists and bloggers covered in 2007-2008 Barack Obama’s voting record in the Illinois Senate on “infant born alive” legislation, a topic that the mainstream media ignored (and haven’t gotten around to mentioning, now that the subject is front and center.) It is that sort of legislation that aims to protect victims like Gosnell’s.

One can suspect this story-selection bias is intentional (delinquencies invariably run in one direction), or one can allow that the lack of geographic, political and social diversity in newsrooms causes the MSM to miss such stories again and again. Either way, the mainstream media swim in a stream of bias, bumping along until their course is altered by outside forces. But the mainstream media can no longer get away with the hide-the-story game for very long. Too many alternative outlets are nipping at the MSM’s heels and carrying news the mainstream media won’t. The mainstream media have, meanwhile, turned off large sections of readers and viewers because they think most of the MSM is in the tank for liberals.

Story selection is the most insidious form of bias and the most dishonest, for it conceals, rather than illuminates, events for the public. With the advent of Twitter, an even worse form of bias has emerged: Mainstream journalists trying to debunk the coverage of conservative outlets of stories the MSM is refusing to acknowledge.

Unfortunately, after each of these non-coverage episodes, we generally don’t see editors being disciplined or outlets hiring more ideologically and culturally diverse reporters. A narrow excuse is devised to justify each episode, but the underlying problem is not addressed. And the mainstream media critics themselves are not interrogated as to why conservative media are doing their job — holding the mainstream media accountable. Maybe MSM outlets should replace them with a link to NewsBusters. Organizations that continually uncover incompetence, error and bad faith in other entities show a shocking lack of self-awareness and accountability when it comes to their own shortcomings.

Now that the Gosnell trial has again highlighted the underlying problem, we’ll be curious to see whether the MSM actually takes the opportunity to address why they didn’t cover Gosnell. It is epsiodes like this that explain why they have become the object of conservatives’ contempt. Refusing to acknowledge the problem isn’t going to help restore their credibility.