Wikipedia was just one of many popular websites that went dark yesterday, in an unprecedented protest against controversial anti-piracy legislation that threatens the open internet — and reporters are scrambling to understand the debate in familiar terms: Is it right vs. left? Silicon Valley vs. Hollywood? But opposition to the Stop Online Piracy Act and its Senate counterpart, the Protect IP Act, is shattering those familiar battle lines.

Back when so-called “network neutrality” regulation was the hot-button technology issue of the day, conservative Republicans such as Rep. Lamar Smith (R‑Texas) urged their fellow legislators to “reject government regulation of the internet.” In 2006, Smith called one neutrality proposal “a regulator’s dream, but an entrepreneur’s nightmare.”

Now, Smith is the lead sponsor of SOPA, a bill that would give the government — and even private companies — sweeping powers to choke off Americans’ access to foreign websites accused of copyright infringement.

SOPA would stifle innovation, stymie free speech and create a powerful incentive for social networking platforms to pre-emptively police their users’ posts, for fear of being branded “rogue sites.”

The last internet regulation this sweeping was seen in 2010, when the Federal Communications Commission ruled to impose the net neutrality regulations that Congress had declined to pass. The rules limit broadband providers’ ability to prioritize or differentiate online traffic.

Supporters thought such rules were needed to protect market competition and prevent large corporations such as Comcast or Time Warner from favoring their own content while slowing potential challengers such as Netflix.

Many conservatives and libertarians, by contrast, worried that net neutrality would open the door to further government meddling.

In response to SOPA and PIPA, however, internet users have let loose the loudest unified roar in the history of the web, with upward of 4 million people e‑mailing or calling their lawmakers in opposition to the legislation.

Civil libertarians of the left and right — such as the two of us, who often disagree on tech issues — have joined forces to decry the legislation’s proposed infrastructure for censorship. Liberal constitutional scholars, including Harvard’s Lawrence Tribe, have been joined in opposition by such conservative legal luminaries as Eugene Volokh and Glenn (“Instapundit”) Reynolds.

One reason the backlash has been so boisterous is that, whereas the net neutrality debate involved a conflict between the values of network openness and limited government, opposition to SOPA unites them. Proponents of openness recoil at the way SOPA lets the government and corporations decide what content users can access.

Unsurprisingly, the old-media conglomerates leading the charge in support of SOPA represent the concentrated corporate power progressives mistrust — but also an undisguised hostility to disruptive power of unfettered markets.

As of this writing, dozens of Republicans who opposed net neutrality are co-sponsors of SOPA or PIPA. Across the aisle, leading lights of the fight for net neutrality such as Al Franken (D‑Minn.) and Patrick Leahy (D‑Vt.) have all signed on as co-sponsors.

Odd as it may sound, given their conflicting philosophies, neither group is holding true to the principles they espouse. Combating online piracy is an important goal, but using government censorship of the internet to do it flies in the face of the values all Americans, liberal and conservative alike, should hold in common.