The idea of copyright (and patents) is to encourage authors by giving them a monopoly over their work for a limited time. The idea is that the benefits of copyright exceed the costs to society of enforcing that monopoly.
The "copyright cartels" of today have warped this beyond all reason. Instead of a limited term of 14 years, they have created copyrights of unlimited duration. Moreover, the costs to society of trying to enforce copyright on the Internet have exploded beyond all reason, damaging both society (by threatening the freedom of speech) and the Internet itself (through regulation and management costs).
The SOPA bill makes all this even worse.
Copyright still makes sense. It's still worthwhile giving authors a monopoly over works for a limited time. It's still worth spending some effort enforcing that monopoly. But not to the degree that it damages our freedoms, and not to the degree that it damages the Internet. Contact your politicians and tell them to vote "no" on SOPA.