It’s for diversity’s sake, he said.

Mark Zuckerberg created a small dust-up this week when he issued a statement explaining why he was allowing Peter Thiel, the controversial billionaire investor and co-founder of PayPal and Palantir, to stay on Facebook’s board despite Thiel’s high-profile support of Donald Trump.

In a post that was leaked to Hacker News, Zuckerberg said, “We can’t create a culture that says it cares about diversity and that excludes almost half the country because they back a political candidate.” In a backhanded defense that is almost comical, he went on to say, “There are many reasons a person might support Trump that do not involve racism, sexism, xenophobia or accepting sexual assault.”

What could those be? One guess is “disruption.” Thiel, like lots of people, likes to blow stuff up in the name of progress, and blowing up the status quo has been, among other things, Trump’s persistent drumbeat. But this is where Zuckerberg’s diversity argument falls apart.

Zuckerberg is in a tough spot. Thiel was Facebook’s first outside investor. He handed over $500,000 in seed money to the college sophomore after a fifteen-minute pitch arranged by the similarly controversial Napster co-founder, Sean Parker. (Read Fortune’s Clifton Leaf’s terrific story of Parker’s attempt to hack cancer here.) Zuckerberg was still in Harvard and Facebook had barely thirty schools on board. Thiel has been an ally from the beginning.

A brilliant and deeply contrarian figure, Thiel has poured his wealth into interesting areas, like paying kids to drop out of college and anti-aging schemes. He even wanted to build an independent, libertarian nation at sea. He’s also expressed alarming views about how welfare and women’s suffrage are ruining democracy, and co-authored a book about how identity politics have destroyed academia. And, of course, he funded the lawsuit that ultimately bankrupted the publishing company Gawker Media Group.

If a Facebook janitor spouted some of Thiel’s harsher stuff at work, she’d get a talking-to from human resources. But that’s the point: These types of idiosyncrasies are typically reserved for the very powerful.

That Zuckerberg uses diversity as the argument to keep Thiel around hits a nerve. The company has struggled to diversify their employee base—even blaming “the pipeline” for their troubles—and has made no visible attempt to change their all-white, mostly male management team or board.

But Zuckerberg has always surrounded himself with philosopher-investors, like Thiel, Parker, Marc Andreessen, and Reid Hoffman, to name a few—brilliant people who hold wildly different world views and love to debate. This diversity of thought should yield better outcomes in tech. But it almost always falls short. Because as different as their individual philosophies are, their collective way of operating—exploit inefficiencies, scale fast, etc.—is largely identical.

President Obama addressed this phenomenon last week at The White House Frontiers Conference, a confab on science and tech, held at Carnegie Mellon University in Pittsburgh:

“Government will never run the way Silicon Valley runs because, by definition, democracy is messy. This is a big, diverse country with a lot of interests and a lot of disparate points of view. And part of government’s job, by the way, is dealing with problems that nobody else wants to deal with.

“Sometimes I talk to CEOs, they come in and they start telling me about leadership, and here’s how we do things. And I say, well, if all I was doing was making a widget or producing an app, and I didn’t have to worry about whether poor people could afford the widget, or I didn’t have to worry about whether the app had some unintended consequences … then I think those suggestions are terrific.

“Sometimes we get, I think, in the scientific community, the tech community, the entrepreneurial community, the sense of we just have to blow up the system, or create this parallel society and culture because government is inherently wrecked.”

That’s Thiel in a nutshell. It’s part of what makes him interesting to have around, whether it’s at a conference or on a board. But “blowing stuff up” doesn’t scale well when it comes to people’s lives. And that makes the Thiel and Trump alliance a luxury I’m not sure most of us can afford.