It's already illegal to market counterfeit and stolen materials in the United States. It has been since, well, the founding of the country. The medium used to do the marketing is immaterial. The Internet isn't new in this regard -- it's simply another means of transport.
In other words, the claimed purpose of SOPA has already been met -- for the last 200 years.
The problem with SOPA isn't the goal. It's the method of enforcement -- or rather, the lack of enforcement.
Sites inside the US that are engaged in these acts can be seized and shut down after and in accordance with due process of law. That's called justice, and it is sometimes applied. It should be applied more often, in fact.
The problem with foreign sites is that the US has no jurisdiction and court orders from the United States are unenforceable. But this does not mean that the United States has no options available to it, or that it should then attack third parties!
SOPA is bad law because it does not stop the production of stolen material, it does not punish those nations that intentionally look the other way at these activities or even explicitly enable and support them and it will do exactly nothing to actually resolve the problem.
The fact of the matter is that the United States could apply punitive tariffs and other trade sanctions against nations that do not respect intellectual property rights.