After the terrorist attacks of 9/11, everyone wanted to know why the people in charge of national security had been caught napping. Various agencies had various pieces of information; why didn't anybody connect the dots?

After Seung-Hui Cho's murderous rampage at Virginia Tech in 2007, similar questions arose. Various individuals had been concerned about Cho's mental state. Why didn't anyone take more steps to forestall the looming tragedy?

It was the same after the Boston Marathon bombing: Why hadn't U.S. officials heeded Russian warnings about the Tsarnaevs?

And after the massacre at Sandy Hook Elementary School in Newtown, Conn., Americans spent a couple months debating whether the nation needed better monitoring of the mentally unstable.

So when alarms went up last year about some potentially ominous postings on Facebook by a Marine Corps veteran, you can understand why law-enforcement agencies thought they should look into the matter.

What happened next is less easy to understand. Or accept.

On August 20, officers from three different agencies – the Chesterfield police, the FBI, and the Secret Service – paid a visit to Brandon Raub, a 26-year-old former Marine with kooky views about the U.S. government. Raub is a "truther" – someone who thinks the federal government was behind the 9/11 attacks – who also thinks Washington's leaders want to "merge the United States into a one-world banking system," and "put computer chips in you," and so on.

On Facebook, Raub had written that "the Revolution is here. And I will lead it." And: "Sharpen up my axe; I'm here to sever heads." The latter turned out to be some rap lyrics – but they take on a new resonance in light of last week's terrorist attack in London.

The authorities interviewed Raub, then took him into custody. But they did not arrest him, and they did not read him his rights. Rather, on the advice of mental-health workers, he was placed under a 72-hour temporary detention order and held for psychiatric evaluation. Four days later, a special justice ordered that he be transferred to another hospital and held for 30 days.

By then the Rutherford Institute, which is based in Charlottesville, had intervened. Attorneys – including former Virginia Attorney General Anthony Troy, working for a private firm – won Raub's release a week after he was taken into custody. Circuit Judge Allen Sharrett found the transfer order "devoid of any factual allegations," albeit largely because of the special justice's failure to check certain boxes on the form.

With the help of the Rutherford Institute, Raub is now suing for violation of his constitutional rights. His district-court complaint makes some valid points – and some others that sound rather less so.

"At no time," it notes, "did Raub make any threat to do harm to any person or to himself." Nor "has any person offered evidence that Raub has harmed or threatened" anyone. Moreover, the mental-health worker who advocated committing Raub did so without having met him. And the strongest evidence for holding Raub even longer? Raub "had long pauses before answering questions" and was "very labile" while being questioned by the Secret Service. (That means he was emotional. Many people would be.)

The complaint also asserts that Raub fell prey to a program called Operation Vigilant Eagle. According to a 2009 article in The Wall Street Journal, Vigilant Eagle tries to head off lone-wolf attacks. It was created as a response to what an FBI memo termed "an increase in recruitment, threatening communications, and weapons procurement by white supremacy extremist and militia/sovereign citizen extremist groups."

Finally, the complaint alleges that federal authorities wanted to label Raub mentally ill "to suppress and chill Raub's political views." They were, it says, "motivated by an intent to retaliate against and suppress" constitutionally protected speech. It's hard to know precisely what the authorities were thinking, because – thanks to Raub's lawsuit – they aren't talking. But that allegation seems too tinfoil-hat to be credible, and is probably a legal tactic to win punitive damages, which depend on a finding of wanton misconduct.

Anyway, motives are largely ancillary. The Cliff's Notes version of the story is straightforward: A U.S. Marine veteran was held against his will for a week on the basis of nothing stronger than vague concerns fueled by some intemperate writings. This bears a distant, yet uncomfortable, echo of Soviet days – when dissidents were consigned to mental wards because, after all, anyone suicidal enough to confront the jackboot of communist totalitarianism had to be nuts.

In trying to distinguish between batty but harmless cranks and genuine fanatics who pose an imminent threat, those charged with protecting America face a serious dilemma. But if their default position becomes broad enough to routinely detain anyone who posts a rambling diatribe on the Internet, then the country faces a policy dilemma as well.