With business as bad as it is, it makes sense for CNBC, the leading business network, to look into an underground enterprise, a vast illegal empire that operates in the warm California sun. “Marijuana Inc.: Inside America’s Pot Industry” (8 p.m., CNBC) offers an hour-long tour of California’s Emerald Empire, located in three counties north of San Francisco where pot cultivation has grown from a casual pastime to one of the state’s biggest cash crops.

Correspondent Trish Regan interviews serious growers and explains the tricky nature of an industry buffeted by overlapping and contradictory county, state and federal laws.

As Regan explains, the economics of pot make it like, well, catnip to some entrepreneurs. The $400 it takes to grow a pound of marijuana can yield $2,500 to a middleman and go for $6,000 on the street. Naturally, an illicit trade and cash transactions lead to violence and gunplay. Regan also interviews a school principal who decided to leave her family’s bucolic neighborhood after she discovered that everybody on her block was in the business.

We also hear from drug-enforcement agents who forage through the remote areas of state and national parks to discover vast pot-farm irrigated with miles of plastic tubing and tended to by diligent farmers who live in underground huts. These extreme outposts appear to be the work of illegal immigrants sent north by Mexican drug gangsters eager to stake a claim in Northern California’s pot bonanza. One of these drug barons, interviewed by Regan, used to import Mexican pot into the San Francisco market but now has to operate closer to his market.

Like many stories on illegal vices like drugs and prostitution, “Marijuana” focuses almost exclusively on the supply side of the business ledger. But what of the demand? Who is buying all of this pot? Should they all be pursued as criminals?

And if, as several officers attest, pot cultivation has, well, mushroomed over the past generation, then what do we make of the billions spent on the so-called war on drugs? Is it folly, or worse?

“Marijuana” cries out for debate. Or at least a few libertarian voices to balance the law enforcement/military approach.

What is the point of treating pot growers like al-Qaida when so many Americans see marijuana cultivation and consumption as their inalienable right? Their pursuit of happiness? How does the war on drugs compare to previous attempts to prohibit alcohol or banish gambling? Does the history of regulating these “sins” offer any lessons? Regan presides over some good footage and interviews a lot of people, but she fails to ask the hard questions.

• The second half of the second season of “Burn Notice” (9 p.m., USA) begins as Michael wakes up after the explosion in his apartment.

Tonight’s other highlights

• Good neighbors inspire good fences on “My Name is Earl” (7 p.m., NBC).

• “Bones” (7 p.m. and 8 p.m., Fox) returns on a new night with back-to-back episodes.

• Betty wants to put her family first on “Ugly Betty” (7 p.m., ABC).

• Langston takes charge on “CSI” (8 p.m., CBS).

• Industrial espionage on “The Office” (8 p.m., NBC).

• Jenna channels a rock legend on “30 Rock” (8:30 p.m., NBC).

• A spring appears to inspire a miracle cure on “Eleventh Hour” (9 p.m., CBS).