When Edward Snowden revealed the depth and breadth of the National Security Agency’s domestic surveillance to journalists a few years ago, the public was shocked — sort of. On one hand, the idea that our government had a bottomless appetite for e-mails, phone calls and texts we once thought private was disturbing. On the other, it was really hard to understand what the NSA was doing and how it was doing it. PRISM? FISA? Somewhere in this alphabet soup was something contrary to life, liberty and the pursuit of happiness, it seemed, if only the common man could bother to be outraged by it.

This was a point driven home by John Oliver, host of HBO’s “Last Week Tonight,” in an interview with Snowden broadcast Sunday. Oliver traveled to Moscow to ask “the most famous hero and/or traitor in recent American history,” as Oliver put it, why he had leaked sensitive government documents.

“The NSA has the greatest surveillance capabilities in American history,” Snowden said, warming up to a subject he has been asked about ad nauseam since he went on the lam. “… The real problem is that they’re using these capabilities to make us vulnerable.”

But Oliver wasn’t there to be lectured. Veering from profane penis jokes to Edward R. Murrow-mode from moment to moment, he challenged Snowden on stories that mistakenly revealed the names of U.S. intelligence agents. It was improper redactions that led to the revelations — but was Snowden, leaker of the information the stories were based on, responsible for what Oliver called a “f—up”?

“You have to own that thing,” Oliver said. “You’re giving documents with information you know could be harmful which could get out there.”

“You will never be completely free from risk if you’re free,” Snowden said. “The only time you can be completely free from risk is when you’re in prison.”

Oliver then played Snowden some “man-on-the-street” interviews that must have depressed the 31-year-old who acted, he said, in the name of his ideals. The upshot, as one interviewee put it: “I have no idea who Edward Snowden is.”

“You might be able to go home,” Oliver said, “because it seems like no one knows who the f— you are and what the f— you did.”

Snowden, laughing, kept his cool — and spoke up for himself.

“I did this to give the American people a chance to decide for themselves the kind of government they want to have,” Snowden said. “That is a conversation that I think the American people deserve.”

Oliver countered that the NSA may be too technical a subject for the public to get riled up about. He likened the debate about government surveillance to a visit from “the IT guy” at work who smells “like canned soup.”

“Is it a conversation that we have the capacity to have because it’s so complicated?” Oliver said. “… Everything you did only matters if we have this conversation properly.”

Oliver then offered a unique proposition: Handing Snowden a snapshot of what Oliver claimed to be his — Oliver’s, that is — penis, he asked Snowden to explain which government programs would have access to the very private photo.

“This is the most visible line in the sand for people,” Oliver said. “Can they see my d—?”

“The good news is there’s no program named ‘The D— Pic Program,'” Snowden said with a straight face. “The bad news is that they are still collecting everyone’s information, including your d— pics.”

Oliver wondered whether, given NSA snooping, everyone should just stop taking illicit photos of their genitalia. Here, Snowden got about as passionate as the pale, stone-faced Snowden gets — and Oliver’s audience responded.

“You shouldn’t change your behavior because a government agency somewhere is doing the wrong thing,” Snowden said. “If we sacrifice our values because we’re afraid, we don’t care very much about those values.”

Cue applause — that seemed to drive home Oliver’s initial point. By putting the NSA debate in terms, however ridiculous, people can understand, Oliver revived it. At least for 24 hours or so.

“I guess I never thought about putting it in the context of your junk,” Snowden said.