In response to that proposal, Jonathan Zittrain, a professor of internet law at Harvard University, wrote an open letter to Cameron, explaining why he thinks it’s a “very bad idea.”

It’s one thing to try and regulate WhastApp, says Zittrain, because the government knows  where Facebook “lives,” and the Silicon Valley company has assets that could be seized.

But what happens when someone produces the next wildly popular messaging app? What if that someone happens to be, as Zittrain wrote in his letter, “two caffeine-fueled university sophomores?” They would be pretty hard to regulate, or even find, according to him.

via Who should have the key to your messages? | Marketplace.org.