When ABC announced in July that Rosie O’Donnell would be rejoining its daytime talk show “The View,” it might have seemed like the program was trying to right course. Barbara Walters had retired. Sherri Shepherd had opted to leave the show as well. And the experiment “The View” conducted with Jenny McCarthy, who has been most prominent for advocating a discredited link between vaccines and autism, did not produce results spectacular enough to overshadow that embarrassment.

Rosie O’Donnell attends “Howard Stern’s Birthday Bash” in New York. (Evan Agostini/Invision/Associated Press)

O’Donnell is a veteran of “The View,” where she frequently clashed with co-host Elisabeth Hasselbeck on various issues, injecting a sharp dose of politics into the show. But in recent days, O’Donnell has provided reminders that she has something in common with one of the women she’s replacing: namely, a tendency towards conspiratorial thinking. McCarthy’s poison is myths about medicine that pose real dangers to public health. O’Donnell, it turns out, does not believe that terrorists attacked the World Trade Center on Sept. 11.

McCarthy has become notorious for her views on vaccination and autism: There is a web site, JennyMcCarthyBodyCount.com, that keeps a grim tally of preventable illnesses and deaths that can be attributed to a failure to vaccinate. But O’Donnell is hardly alone in embracing Sept. 11-related conspiracies in the name of rationalism and scientific inquiry. Such perspectives show up with some regularity in the entertainment industry, and holding them has not exactly made their adherents marginal figures.

Roberto Orci, the prolific Hollywood screen and television writer and producer, has expressed skepticism about what happened on Sept. 11. The actor Daniel Sunjata is a fan of the truther movie “Loose Change” and  has appeared on conspiracy theorist Alex Jones’s show. Jones cheerfully described Sunjata as “prominent 9/11 truther” and gave Sunjata credit for advocating for the inclusion of 9/11 conspiracy story lines in the show “Rescue Me.” Ed Asner has made a taped statement raising 9/11 truther questions in a video addressed to the federal commission responsible for investigating the attacks. Martin Sheen credited his son Charlie with convincing him to take questions about the official narratives of the attacks more seriously.

It is easy to see why vaccine denialism elicits such disgust. The American public loves judging other people’s parenting decisions, and there are fewer clear-cut opportunities for judgement than a choice that puts children in active danger or that shifts risk onto other families. Criticizing McCarthy’s role in a rising public health danger is an opportunity not just to accuse her of faith in bad science but, worse, of being a Bad Mother.

But vaccine deniers and 9/11 truthers have a great deal in common.

Both claim the imprimatur of science. Vaccine deniers cite a retracted study published in the Lancet in 1998 that claimed to demonstrate a link between vaccination and incidences of autism. Sept. 11 truthers claim the mantle of scientific authority for themselves by claiming they are the only people interested in posing serious questions about the science behind the collapse of the World Trade Center towers (an issue that comes up in O’Donnell’s tweets). This is a dangerous inversion of scientific thinking and the scientific process, suggesting that science can only be valid if it produces the results the movements want to see.

Both are suspicious of authority. Vaccine deniers see requirements for vaccination as originating in a sinister conspiracy between the Centers for Disease Control and Prevention and pharmaceutical companies. Sept. 11 truthers suggest that the attacks were in the interests of either certain people in the federal government or shadowy financial interests who profited from shorting airline stocks.

There is nothing wrong with a reasoned skepticism of the government or the motivations of large corporations. But there is surely a reasonable line to draw between observing reality carefully and living in fantasyland. It may be a quicker step between the magical thinking of vaccine denialism and its consequences than 9/11 trutherism and its downstream effects. Those consequences do exist, though: Cliven Bundy’s standoff with the federal government draws from the same fetid pool that lead some Americans to believe that federal officials would murder thousands of U.S. citizens for their own gain.

We should not let gender politics or the glee of judging others’ parenting lead us to treat these kinds of conspiracy theories differently. “The View” may have traded in an anemic host for one with a more proven track record, but the show has also continued a subtle endorsement of a very ugly kind of thinking.