It is, but our judges and legislators find it expedient to pretend it's not.

The people who wrote it and the people who ratified didn't seem to think it was absolute. The First Amendment was not intended to create a new right of speech. It was intended to prevent the new federal government from abridging the existing right as it was under common law and state law.

Under state and common law at the time many kinds of speech were routinely regulated or even criminalized, such as defamation and blasphemy.