The Washington Post, as part of its ongoing web redesign, unveiled an addition to its online opinions section on Monday. Now there are tabs for left-leaning columnists and right-leaning columnists; you can even subscribe to ideologically segregated RSS feeds. The change drew jeers from wags such as Gawker’s Hamilton Nolan, who complained that the tabs will allow a reader to “comfortably segregate yourself in the opinion ghetto of your choice.”

The tabs may indeed be silly—they certainly are flawed—but not because they allow readers to ignore opinions with which they disagree. Readers have always had the option of skipping over columns that are ideologically or stylistically uncongenial, and readers have always done so. The Internet and cable news have magnified this trend in any number of ways, and the Post’s tabs are—relative to the rise of partisan blogs, right-talk radio, FOX News and MSNBC—the smallest possible contributor to the problem of “epistemic closure.”

Rather, the Post’s tabs are troublesome because they expose the flawed measure that the mainstream media uses to quantify ideological diversity. Left versus right is only one of the ways that columnists can vary in their orientation, and arguably it is one of the less important. What really makes an op-ed page useful is when it presents writers from diverse backgrounds. This can mean many things, not just gender and ethnic diversity—although the Post opinion stable is severely lacking on both of those counts. The Post has thirty opinion writers and bloggers of whom only six are women and only five are non-white. That means nineteen of the thirty, almost two-thirds, are white men. Whatever their partisan preferences, this is not representative of America, nor Washington, D.C.

On other metrics the Post performs as badly or worse. Take age: it appears that only three of the Post’s opinionated voices—Ezra Klein, Jonathan Capehart, and maybe Greg Sargent—are under forty years old. And what about areas of expertise? The vast majority of the Post’s opinion writers are former political reporters. A few cover policy and came from magazines. A couple have been political activists: Michael Gerson worked in the Bush White House and Harold Meyerson worked in the labor movement. Almost none—Charles Krauthammer, who was a psychiatrist and a White House science advisor more than three decades ago, is the only apparent exception—have professional expertise in a technical field outside of journalism.

At a time when op-ed pages swirl with debate on complex matters of economic policy and financial regulation, climate change and energy policy, and rampant revolutions in the Middle East, the Post might benefit from focusing less on balancing partisanship and more on balancing expertise. Take The New York Times, for example, which since 2000 has published regular columns by Paul Krugman, a Nobel Prize winning economist. Obviously, not every paper can snag a Nobel laureate for its op-ed page—but the idea of selecting columnists who are recognized experts in their fields is an ideal model that could replicated at other papers and across all disciplines.

By making partisan affiliation the primary qualification of an opinion writer, one risks running hogwash like George Will’s ignorant, dishonest climate change denial. The relevant question on whether carbon emissions are causing global warming isn’t what political liberals or conservatives think about that, it is whether it is happening. How about having a climate scientist, or a reporter who covered science, weigh in on the topic, rather than a political columnist?

The other problem, which Nolan hints at by mentioning “left-leaning” Post columnist Richard Cohen’s attacks on Wikileaks, is that political columnists cannot always be so easily categorized. Cohen writes from a hawkish, center-left contrarian vantage point that is shared by relatively few Americans but quite a few political columnists, including others at the Post. Thus Cohen, like Zakaria and The New York Times’s Thomas Friedman, supported the Iraq war. Like Joe Lieberman, these writers would be assigned to the left on a binary scale because they believe in global warming, presumably support abortion rights (although they never write about that), and usually support Democrats. But to present them as unmitigated representatives of the left is a misleading categorization that obscures more than it illuminates.

Ben Adler covers climate-change policy for Grist and is a contributing editor for CJR