In a much praised article, Chris Mooney writes in Mother Jones about "The Science of Why We Don't Believe in Science" in which he explains why Republicans hate science. To be fair, he then goes on to ask:
So is there a case study of science denial that largely occupies the political left? Yes: the claim that childhood vaccines are causing an epidemic of autism. Its most famous proponents are an environmentalist (Robert F. Kennedy Jr. ) and numerous Hollywood celebrities (most notably Jenny McCarthy  and Jim Carrey). The Huffington Post gives a very large megaphone to denialists. And Seth Mnookin , author of the new book The Panic Virus , notes that if you want to find vaccine deniers, all you need to do is go hang out at Whole Foods.
Right! Autism and vaccines is the example of science denial on the left. What else is there? The hounding of James D. Watson and Larry Summers out of their jobs for politically incorrect statements about the science of intelligence pales in comparison to the actions of noted leftwing intellectuals Jenny McCarthy and Jim Carrey regarding autism.
Look, the people who are most worked up over the theory that vaccines cause autism are the parents of children with autism. It's not a left wing plot or the failure of leftist ideology. It's a bunch of parents with tragic problems that mainstream science hasn't done a good job of explaining. (Jenny McCarthy has an autistic child and Jim Carrey was her boyfriend for a while.) They latched on to an idea that wasn't terribly implausible at the beginning, which gave them a little hope, or at least some notion of cause and effect. It didn't turn out to be right, but that doesn't have much to do with the Left.
You can't make the same excuses, however, for the most honored commissars of political correctness, such as Stephen Rose and Morris Dees.