Mark Zuckerberg recently embarked on a laudable, altruistic mission to bring Internet to the 5 billion people in the world who don’t have it. But here’s what the Facebook CEO's white paper didn’t tell you: If 5 billion new people got online, Facebook could make in the ballpark of $3.5 billion in the first quarter.

That won’t surprise cynics who smelled a lucrative business opportunity in Zuckerberg’s talk of “connectivity” and “human rights.” (The Washington Post’s Hayley Tsukayama called it a “long play” in Facebook’s ongoing quest for more users -- and ad revenue.) That business opportunity will lie largely in mobile, since most people in developing countries get Internet through their phones. Marco Veremis, the CEO of mobile monetization firm Upstream, runs the numbers this way: 5 billion x $0.7, the median average revenue per unit in Asia and emerging markets = $3.5 billion per quarter, or $14 billion per year. Average revenue fluctuates, of course, so that's approximate.

“This is why Facebook is leading the new initiative to give affordable mobile access to all consumers in developing markets,” Veremis wrote in an e-mail. “[It’s] a strategic move to establish Facebook as the main portal in consumers' minds.”

Of course, whatever the scale of Facebook’s efforts, it’s unlikely that 5 billion people will actually get online, cautions Nate Elliott, an analyst at Forrester who focuses on social media. Even in developed markets, total online adoption is around “80ish percent.” And plenty of people are on Facebook in emerging markets already, 100 million on feature phones alone. So while Zuckerberg has talked a lot about “the next 5 billion,” Facebook realistically stands to add fewer users than that.

In India, for instance -- a country with 1.24 billion people -- total online penetration hovers around 27 percent, according to Forrester. Getting to 80 percent would mean adding 657 million people, with gains of roughly $490 million per quarter (almost $2 billion per year) for Facebook, assuming a $.75 ARPU.

Does that mean Zuckerberg doesn’t have the human rights of the world’s disconnected at heart? Not necessarily. But as Tsukayama noted on Wednesday, “it’s more lucrative to have more people using the Internet” than less.