Whatever happened to the old journalistic adage that “if your mother tells you she loves you, check it out”? These days, too many reporters imagine their primary role is to police public discourse about the news — rather than, well, reporting the facts.

Witness the mainstream media’s rush to tsk-tsk the deluge of social-media speculation in the aftermath of Jeffrey Epstein’s death in federal custody. Within hours of the story breaking, writers at mainstream outlets went patrolling the Internet for “conspiracy theories” to debunk, usually with that tone of superiority and self-satisfaction that so endears the blue-check Twitterati to the American public.

“Suicide is the leading cause of death in US jails,” scolded The Daily Beast’s Justin Miller. “ ‘Suicide watch’ is just that, ‘watch,’ or observation, usually periodic. Stop speculating Epstein was murdered.” The headline on a story by Miller’s colleague Kelly Weill read: “Conspiracy Theories Erupt After Jeffrey Epstein’s Death.” (Talk about begging the question.)

“It would be easy to treat this frenzied reaction to Epstein’s death as a sad case study in how conspiratorial thinking has bled into mainstream discourse,” lectured The Atlantic’s McKay Coppins. “But finger-wagging feels inadequate at this moment.”

Among other examples of this lamentable rise in paranoia, Coppins cited one of my tweets. In it, I had recounted how a Manhattan restaurateur I know predicted that “they’ll never let Epstein live” — “they” being our shady ruling class. “Regular people,” I added, “are wiser than us pundits.”

If Coppins had bothered to contact me for comment before writing critically of my remarks — as is standard journalistic practice — I would have told him that, of course, I don’t necessarily believe the restaurateur was right. But at the time I heard him say it, I was inclined to dismiss the restaurateur’s cynicism about our system. “What does he know?” I thought. “Of course, Epstein will live to testify.”

Well, events seem to have vindicated the more cynical view of how the American system works, even if we still don’t understand the full factual circumstances of Epstein’s demise.

Speaking of which, shouldn’t the reporters who are busy lamenting our nation’s conspiratorial cast of mind wait for the facts to come out? After all, at least three local and federal probes have just gotten underway. The Justice Department and the Bureau of Prisons have been careful to append the adjective “apparent” to the noun “suicide” in their statements on the matter. As Will Chamberlain of Human Events noted, the no-conspiracy journalists are “ahead of the facts.”

It’s all especially rich, given the fact that many of these same journalists have spent the past two years feverishly promoting the “collusion” theory. Here’s Coppins writing in 2017: “As evidence piles up pointing to the possibility that the Trump campaign colluded with Russia, Republican lawmakers have largely ignored Democrats’ calls for urgent action.”

Actually, there was no evidence of collusion, as the Mueller report concluded. But don’t expect Coppins to take responsibility for injecting “conspiratorial thinking . . . into mainstream discourse.”

Sohrab Ahmari is The Post’s op-ed editor.