Sometimes false equivalencies come from the most unexpected sources.
In 2008, the always vitriolic and reliable Matt Taibbi released his book The Great Derangement in which he looked at the growing disconnect between the American electorate and reality/facts. For reasons never explained and certainly not justified by reality, he presented End Times Christianity (and all the beliefs like creationism that accompany it) and 9/11 Trutherism as opposite ends of the political spectrum. That is, what creationism and fundamentalism are to The Right, Trutherism is to The Left. This is so far beyond stupid that I still can't believe he, of all people, wrote it. Trutherism is and always has been a movement of the Alex Jones crowd, the ultra-survivalist paranoid types who, if anything from the normal realm of politics can be applied to them, are closer to Libertarians than Liberals. They are a loose collection of conspiracy theorists, anti-government types, and good old fashioned charlatans and rubes. So to call Truthers the Christian fundamentalists of The Left is beyond a stretch – it is just false.
Had he waited a couple years or done a bit more research, he would have realized that the actual left-wing version of right-wingers who think the planet is 6,000 years old are the anti-vaxxers. This is not to say that all anti-vaxxers are liberals, as a good portion of them harbor some level of "Ain't no gubmint gonna tell ME what to do!" motivation. But if you want to point to something absolutely, categorically false and stupid that has a decent amount of popularity on the left (primarily among the Mother Earth Hippie liberals), crackpot vaccine theories are a much better fit for Taibbi's analogy. As a recent editorial puts it, the anti-vax movement is driven almost entirely by "Rich, educated, and stupid" parents. In other words, it is driven by people who should know better but don't; who have so bought into the idea of all things Natural being inherently superior that they have knee-jerk reactions against anything pharmaceutical or chemical entering the body. An author astutely called Whole Foods the "temple of pseudoscience" earlier this year, and although it pained many of my friends and colleagues to admit it, that is not inaccurate. Objectively, nothing separates the touted "holistic" and "natural" cures for various health issues from snake oil salesmen on infomercials. Or from the kind of awful science practiced by the religious right.
For the kind of person who believes that a bunch of herbal supplements* can cure your ailments "Nature's way," the intellectual leap to anti-vax arguments is not very far. That movement ties together several strains of American political paranoia – the distrust of Big Corporations, the insistence that things were so much better in the good ol' days, and the insistence that thanks to the internet, we all know better than any "expert" excepting of course the self-identified ones who tell us that what we believe is correct. It is popular among liberals, myself included, to take great joy in mocking the various stupidities of modern conservative ideology. We are less eager, logically, to point out that different flavors of that same poisonous logic pop up on the left as well. There are knuckleheads among us, and they sure as hell aren't talking about 9/11.
*This is not a blanket statement implying that there is no value in non-pharmaceutical medicine or that no conditions can be treated "naturally". It is instead an argument that the vast majority of what are offered as natural or herbal remedies have no scientific evidence to support their claims whatsoever – a problem endemic to the unregulated "dietary supplement" industry.