This is a video, posted on Monday to Facebook, of one of Syria's stronger rebel factions setting a marijuana field ablaze. The incineration of the weed underscores a basic problem for the U.S.'s approach to Syria's bloody civil war.

No, not because the U.S. suddenly decriminalized marijuana. It's because the Farouq Brigades, generally considered a competent and media-savvy rebel militia, is promoting its willingness to destroy a drug crop. That's an action usually identified more with Islamic militant groups than secular ones. And it goes to show how little the U.S. still knows about the Syrian opposition, even as Washington debates directly arming the rebels.

It's a problem that cuts across political boundaries. The Obama administration is helping Persian Gulf states maintain a weapons pipeline to the rebels, even as Pentagon officials acknowledge the risk of those weapons spreading outside Syria to destabilize the region. Supporters of broadening U.S. aid to the rebels, like Rep. Buck McKeon, the chairman of the House Armed Services Committee, concedes that he doesn't know what the true agendas of the rebels are, beyond overthrowing dictator Bashar Assad. Mitt Romney wants to only arm those rebels who "share our values."

Easier said than done. It's not necessarily that the U.S. lacks data on the various Syrian factions. Some groups, like the Farouq Brigades, put out a ton of information on websites and Facebook page. It's just that there aren't clear conclusions to be drawn from the data about the factions' intent for a post-Assad Syria. "It's very complicated, trying to say how Islamist these specific groups are," says Jeffrey White, a former U.S. defense intelligence officer who studies the Syrian civil war at the Washington Institute for Near East Policy.

The Farouq Brigade is especially competent at getting its message out. Its Facebook page features a new video practically every day, showing militiamen firing heavy anti-aircraft guns and giving interviews to major media. They've allowed reporters from Western news outlets to embed with them: Earlier this month, the Farouq Brigades took Time on a ride-along, resulting in a piece that called them a more "professional fighting force" than other groups fighting under the Free Syrian Army banner. Indeed, they rose to prominence during February's siege of Homs, helping hold off Assad's forces in the Baba Amr neighborhood for a month, and control several checkpoints along the Turkish border – an indication of their access to heavy weaponry, unlike other factions who have to homebrew their own. Estimates of the Farouq Brigades' size vary widely, from under 4,000 to 20,000; credible estimates are hard to find.

So are credible estimates of its ideology. Time reported that a Farouq Brigade commander criticized al-Qaida, but noted the commander's own "neat Salafi-style black beard," a suggestion of deeper militant Islamist leanings. A Farouq fighter interviewed by the U.K.'s Channel 4 last month complained that the West wasn't arming the group "because of the religious way we look."

Both White and Joe Holliday, a research analyst watching Syria for the Institute for the Study of War, consider the Farouq Brigade "moderately Islamist" – that is, neither secular nor Salafi. They don't employ the hardcore tactics of the jihadis, like suicide bombings or stuffing captured government soldiers into trucks filled with explosives. And while some of their fighters wear black headbands of jihadis and display "these types of jihadi symbols in their appearance," Holliday says, "it's hard to parse out whether that's just the style right now."

In Syria, even being a "moderate Islamist" group, whatever that actually means, isn't necessarily a fixed position. It could just as easily be a branding of convenience for organizations seeking access to weaponry – from whatever source. "The question is, is that a cover for getting weapons and aid [from Gulf states], so they're not really Islamist very much at all; or are they really Islamist and pretending to be moderate?" White says. "No one knows for sure." And that's after studying the groups' actions and statements for months.

Which means U.S. policymakers don't have much hope of clearing away the fog around the Syrian rebellion. Shoveling arms to groups with murky motivations has a new urgency now that shadowy factions destroyed the U.S. consulate in Benghazi, Libya, a city the U.S. helped save from Moammar Gadhafi last year. On the other hand, the Syrian civil war has taken approximately 30,000 lives in the past year and a half.

Figuring out what to do about the slaughter can often depend on how analysts interpret images like the ones showing a zealous band of fighters burning a marijuana crop. "That's suggestive of Islamist tendencies," White says, "the counter-drug, antinarcotics piece of it." If the U.S. ultimately chooses to throw in its lot fully with the Syrian rebels, these may be the people it arms.