Kurt Andersen has a guest column in the New York Times today, and about four-fifths of it is terrific. There’s just one thing missing.

Andersen argues persuasively that there’s an “epidemic in mainstream politics,” driven by those who “inhabit their own Manichaean make-believe worlds.” People like Rick Perry and Michele Bachmann, he added, “totally believe their vivid fictions.” I couldn’t agree more.

The column goes on to diagnose what Andersen sees as a national disease: “[T]he American body politic suffers from autoimmune disorders.”

At some point, our bodies’ own immune systems went nuts, mistaking healthy pieces of our anatomies — a pancreas, a thyroid, a joint — for foreign tissue, dangerous enemies within, and proceeded to attack and try to destroy them. It’s as close to tragedy as biology gets.

Which is pretty much exactly what’s been happening the last decade in our politics. The Truthers decided the U.S. government was behind 9/11. Others decided our black president is definitely foreign-born and Muslim. Tea Party Republicans are convinced his administration is crypto-socialist and/or proto-fascist. The anti-Shariah people are terrified of the nonexistent threat of Islamic law infecting American jurisprudence. It’s now considered reasonable to regard organs and limbs of the federal government — the E.P.A., the education department, the Federal Reserve — as tumors that must be removed. Taxation itself is now considered a parasitic pathogen rather than a crucial part of our social organism.

Many autoimmune diseases of the literal kind, such as Type 1 diabetes and multiple sclerosis, are apparently triggered by stress. For the sociopolitical autoimmune epidemic, there are plenty of plausibly precipitating mega-stresses: the 9/11 attacks and the resulting wars, a decade of stagnant incomes, chronic job insecurity, hyper-connected digitalism, real estate wipeout, teetering financial system, take your pick.

The larger point, and the metaphor itself, strikes me as entirely compelling. There is a deep strain of madness that’s come to dominate much of our discourse and the political world, and the way in which facts, reason, and evidence are constantly under attack does look quite a bit like an autoimmune disorder.

At the risk of sounding picky, my nagging concern is over the false equivalency. Truthers, racists, Tea Partiers, and the anti-Shariah crowd all believe and are driven by nonsense, but they’re not relative equals in size, scope, power, or influence.

On the contrary, on the left, there is a liberal fringe, but it’s ignored and kept at arm’s length by the progressive mainstream and the Democratic Party. On the right, radical conspiracy theorists don’t just have a prominent voice; they wield enormous influence in the Republican Party and occasionally get elected to powerful public offices. Indeed, in the case of the Republican presidential field, Perry and Bachmann routinely spout surreal gibberish, and they’re two-thirds of the GOP’s top tier.

To my mind, one of the fundamental problems with American politics isn’t the existence of a right-wing fringe, it’s the fact that the line between the fringe and the GOP mainstream has been blurred. Both sides have nutjobs; only one side thinks their nutjobs are sane.

To use Andersen’s metaphor, it’s the difference between an autoimmune disorder that’s temporary and inconsequential, and one that’s life-threatening. It’s a difference worth appreciating.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.