The Internet, as of this writing, is an anarchic system. While there are certain regulations and norms that govern behavior, they are not strong. There is no individual or subset of individual users/developers who can claim legitimate authority to coerce others over the Internet. For now, it remains free.
The Stop Online Piracy Act (H.R. 3261, and its Senate counterpart, S. 968) represents a threat to that freedom. If this legislation were to pass into law, it would be widely regarded as legitimate not because of any inherent rightness, but because of the power of the body that enforces it. The authors of this bill likely do not realize that it will fail in its stated goal--to prevent copyright-infringing downloads--while at the same time perpetuating the falsehood that there is an exclusive property right to truth.
Law certainly has a legitimate role to play in society: to clarify expectations. But our societal expectations regarding intellectual property have already been stated in existing copyright law--which SOPA will not strengthen or improve in any way. In fact, the harm of expansive, one-size-fits-all copyright is already evident from the fact that many works whose authors have long since passed away are still not part of the public domain in the US. The Internet evolves extremely quickly, while legislation tends to come about in punctuated ways. Once SOPA or a similar law is on the books, it will be tremendously difficult to modify in light of changing circumstances.
Web developers, writers, and everyone else who blacked out their pages this week to demonstrate opposition to SOPA proved at least one thing: the Internet community is capable of overcoming collective action problems. If SOPA is stopped, there will not be any one single person or group to thank. It will be because all of us banded together to show that freedom still exists. For now.