Way back on Feb. 23, The Post ran an opinion piece by Steven Mosher saying that we couldn’t trust China’s story about the origins of COVID-19. He argued that the virus might — might — have jumped to the human population thanks to errors at a Chinese laboratory in Wuhan, rather than via that city’s now-notorious “wet market.”

The piece was widely read online — until Facebook stepped in.

The social media giant’s “fact checkers” decided this was not a valid opinion. If you tried to share Mosher’s column on Face­book, the social network stuck a “False Information” alert on top, saying that finding was “checked by independent fact-checkers” and preventing your friends from clicking to connect to the original article to see for themselves.

Again, this was an opinion column, not a news report.

Mosher cited a host of suggestive facts, including urgent government directives, the sudden trip of China’s top biowar expert to Wuhan and that nation’s shoddy record of lab safety — as well as gaping holes in the wet-market explanation, such as the fact that the market in question doesn’t sell bats, the animal from which the bug supposedly jumped.

How, exactly, did Facebook determine that Mosher’s reasoned arguments constituted “False information”? Well, in fact, it didn’t so determine: Rather, it was an “independent fact-checker.”

And who did this fact checker rely on for their opinion? As reporter Sharyl Attkisson notes, one expert consulted had a clear conflict of interest: She has regularly worked with Wuhan’s researchers, and even done her own experiments there. Danielle E. Anderson, assistant professor, Duke-NUS Medical School in Singapore, personally attested to the lab’s “strict control and containment measures.”

Anderson did admit, however, that Mosher was correct when he mentioned that SARS did twice escape a Beijing research lab in 2004.

The other expert who weighed in noted in her objection: “Any responsible government would strengthen safety and security procedures in high-containment labs that will and should be working with the novel coronavirus to develop countermeasures and diagnostics.”

Well, yes, any responsible government would.

Because these medical researchers took offense that someone would question the Wuhan lab’s protocols, Facebook decided you weren’t allowed to speculate online.

Nearly two months later, of course, Mosher isn’t alone in his opinion.

This week brought hard news in the form of State Department cables from January 2018 showing that the US government had longstanding, grave concerns about safety protocols at the Wuhan lab — China’s only Level 4 biohazard laboratory.

And multiple outlets, including Fox News and The Washington Post, report that top US national-security officials are increasingly of the belief that the bug came from that lab.

The New York Post has asked for weeks to get Facebook to un-block the Mosher article. On Friday, the social network finally did so, though without acknowledging that it had been wrong all along.

As a significant source of news for much of the world’s population, Facebook has a clear responsibility to do better: If it’s going to block “false” information, it needs better fact-checkers — and more people watching over those watchmen.

When your defense against “fake news” all but kills free discussion, your system is worse than no defense at all.