Almost everyone agrees that unlocking your cellphone should be legal. But crafting legislation to give consumers the freedom everyone agrees they should have is surprisingly difficult.

The debate over cellphone unlocking started about a year ago, when a ruling by the Library of Congress suggested that unlocking your cellphone to take it to another wireless carrier could run afoul of copyright law. That triggered a grassroots backlash, prompting members of Congress and even the White House to support overruling the Librarian's ruling.

But crafting legislation to permit cellphone unlocking has been surprisingly complicated. Rep. Bob Goodlatte (R-Va.), the chairman of the House Judiciary Committee, has introduced legislation permitting consumers to unlock their cellphones. But that legislation has gotten lukewarm support from public interest groups who say it doesn't go far enough in recognizing consumer rights.

On Friday, the advocacy group Public Knowledge announced it was withdrawing support from Goodlatte's bill after the chairman introduced a new version. The new version includes language permitting individuals to unlock their cellphones. But the legislation states that "nothing in this subsection shall be construed to permit the unlocking of wireless handsets or other wireless devices, for the purpose of bulk resale."

The problem, according to Public Knowledge's Sherwin Siy, is that the DMCA shouldn't apply to phone unlocking—"bulk" or otherwise—in the first place. The DMCA was supposed to be about preventing piracy, not limiting what consumers do with their gadgets. The new Goodlatte bill "doesn't prevent bulk unlocking but it certainly seems to suggest Congress thinks it's already prohibited," Siy says. That could be a step backwards.

The issue has significance well beyond cellphones. More and more of the products in our daily lives have computers embedded in them. If it's illegal to unlock your cellphone, it might be illegal to modify or repair a wide variety of other products. For example, all modern cars have computers embedded in them, and repairing a car increasingly requires accessing its onboard software. Could car manufacturers invoke the DMCA to prevent unauthorized repair work?

An aide to the judiciary committee insists that critics like Siy are over-reading the legislation. The bill is intended to allow cellphone unlocking, the aide says, without affecting broader questions about the scope of the DMCA. Those broader issues will be tackled later, as part of a broader review of U.S. copyright law.

But the current furor over cellphone unlocking represents a rare opportunity to craft DMCA reform that could actually pass Congress. If Congress passes narrow legislation fixing only the most obvious abuse of the DMCA, there might not be enough political capital left for a broader reform later on.

The Electronic Frontier Foundation, another public interest group that favors overhauling the DMCA, shares Siy's concern. "We are deeply concerned that the bill has new language excluding bulk unlocking," EFF's Corynne McSherry says. "Unlocking, whether individually or in bulk, makes reuse and repair possible, and is a public benefit. It should be clearly lawful."