Random Constitutional Thought

With all this talk of Supreme Court justices who should be "strict constructionist", I always scratch my head at the "literal text" of the free speech portion of the First Amendment. It reads "Congress shall make no law . . . abridging the freedom of speech." If we read the text literally, it should be unconstitutional for Congress to enact any law regarding libel or slander, threats, pornography, or the overthrow of the government. That is, no law should be enacted which in any way abridges speech. That's what the constitution says, doesn't it? I suppose "liberal, activist" judges have somehow placed limits on that clause.