SAN FRANCISCO — Peter Thiel has caused a ruckus in Silicon Valley. In recent months, the controversial investor has thrown his weight behind the presidential candidacy of Donald J. Trump — making him a rarity among the technology industry’s elite.
Over the weekend, he backed that up by giving $1.25 million to support the candidate, drawing the ire of Silicon Valley’s many Trump critics and forcing tech executives who work with Mr. Thiel to explain why they plan to continue doing business with him.
Earlier this week, Mark Zuckerberg, Facebook’s chief executive, took to his service to defend Mr. Thiel’s seat on the company’s board of directors. Mr. Zuckerberg warned that severing ties with Mr. Thiel because of his political views would be a troubling precedent, echoing an earlier defense of Mr. Thiel’s continued involvement with the tech start-up organization Y Combinator.
“We care deeply about diversity,” Mr. Zuckerberg wrote in an internal Facebook post addressed to employees. “That’s easy to say when it means standing up for ideas you agree with. It’s a lot harder when it means standing up for the rights of people with different viewpoints to say what they care about. That’s even more important.”
On Tuesday, an image of Mr. Zuckerberg’s message was posted to the website Hacker News, an online forum popular in technologist circles. Facebook confirmed the veracity of the photo and the post but did not comment further.
Though Mr. Zuckerberg did not say he agreed with Mr. Thiel’s decision in his post, which went up a few days after The New York Times reported the donation, he warned that accepting differing political viewpoints was an essential part of Facebook.
Mr. Zuckerberg’s words echo a sentiment from Sam Altman, the managing director of YC Research at Y Combinator. Mr. Altman, who has invested millions of his own money in a campaign to turn out young voters, defended Mr. Thiel’s position as a part-time partner at Y Combinator, a position he took last year.
“Thiel is a high profile supporter of Trump. I disagree with this,” Mr. Altman wrote in a series of Twitter posts on Sunday. But “YC is not going to fire someone for supporting a major party nominee.”
He added: “Diversity of opinion is painful but critical to the health of a democratic society. We can’t start purging people for political support.”
Mr. Zuckerberg has alluded to his opposition to some of Mr. Trump’s policies, once condemning Mr. Trump’s call to “build a wall” to stem the tide of illegal immigration from Mexico.
But in recent months he has guarded his political beliefs more closely, especially after claims were made that some conservative viewpoints were being blocked from wide visibility across the network by Facebook employees.
Mr. Zuckerberg now walks a fine line between what he describes as adhering to Facebook’s core values of sharing and diversity of opinion while trying to avoid rankling the thousands of people he employs.
“We can’t create a culture that says it cares about diversity and then excludes almost half the country because they back a political candidate,” he wrote.
Not all tech industry figures are as accepting of Mr. Thiel’s enthusiastic support for Mr. Trump. Earlier this week, Ellen Pao, the head of Project Include, an organization that is trying to increase diversity in the tech industry’s work force, said her group was severing ties with Y Combinator because of Mr. Thiel’s involvement.
“We agree that people shouldn’t be fired for their political views, but this isn’t a disagreement on tax policy, this is advocating hatred and violence,” Ms. Pao wrote on the site Medium.