[Coda]

It's not an impossibility. The courts would have to fight out whether or not just links could be considered infringement, but the precedent is there.

To answer your question: DMCA handles domestic sites just fine. SOPA is primarily targeting foreign websites that DMCA doesn't cover, in sections 102 and 103. The big deal for US domestic sites is SOPA section 201, where the very definition of what constitutes infringement is broadened -- SOPA's true purpose is to give big companies a weapon to criminalize what would usually be a civil matter, under the guise of making the definitions broad enough to cover "loopholes" in existing law.