Huffington Post appears to have drawn the line on acceptable political debate to exclude theories about the nativity of Sarah Palin's youngest son.

Palin critic Geoffrey Dunn, who has contributed a long line of attacks on the former Alaska governor to the site, published his version of the "Trig Truther" theory to Business Insider today, after Huffington Post turned the blog post down.

"We did pass on a submission by Geoffrey Dunn about Trig, as it ran counter to our policy against conspiracy theories," Huffington Post spokesman Mario Ruiz confirmed in an email. 

There's a solid bipartisan tradition of such purges, which includes in the online era the DailyKos ban on 9/11 Truthers and RedState's Birther ban. But the Trig theorizing had mostly avoided that fate, partly because it never developed the sort of mass following of the others, partly because there's so much vitriol for Palin on the left and partly because its most visible proponent, Andrew Sullivan, is a unique media property with a large audience of his own, valuable enough to the Daily Beast that they'll shrug off the Trig theories as an eccentricity as long as his readers abide it.

The theories of Trig's nativity seem -- to my nonexpert eye -- to share one thing in particular with the conspiracies about Obama's birth: They began in one form, then changed to evade inconvenience facts. In Obama's case, there were debunked Muslim rumors and ill-informed notions about the law of citizenship; people who wanted to believe Obama was a foreigner only settled on the birth certificate nonsense late, after those had dead-ended.

Palin's case seems simpler: There were rumors (true) that her daughter was pregnant, which generated (as Frank Baley wrote in his mostly anti-Palin book) rumors that Palin was actually claiming her grandchild as her son. This wouldn't be an outlandish theory, and she wouldn't have been the first mother to have done so. The theory also had its grain of truth in the fact of Bristol's pregnancy. But then Bristol had a baby, and the whole theory should have, by all rights, collapsed. Instead, it evaded Occam's razor and reshaped itself in a more complex form.

In any event, if Palin decides to run for president, she'll if anything benefit politically from attacks on her motherhood. Indeed, Palin's allies online are spending today denouncing -- and drawing attention to -- a blog's attack on her son. And of course popular disgust with such attacks won't stop them: Alex Jones, Jerome Corsi, Donald Trump and many others are presently demonstrating the eternal truth that there's a market for ugly theories about polarizing figures.

Palin might also, with the same bad taste in her mouth that Obama felt in the summer of 2008, release the birth certificate. But as Obama found, at some point the conspiracy train has left the station and at least some of its believers can't be stopped by mere proof. 

NOTE: Sullivan and Dunn say Dunn isn't suggesting Palin's not Trig's mother. He's just, like Donald Trump, asking questions, and making suggestions, such as that "the American media should demand that Palin produce full and conclusive evidence of Trig's birth and parentage."