The criminal code describes specific protected categories & speech and, if it becomes unclear, the courts determines the specific line in individual cases. In some cases it goes to the supreme court to set a general standard.

Typically it's up to the society's jurisprudential body to determine if harm has been caused in each individual case, the same way damages are determined in most infringements - i.e. slander, libel, defamation, obscenity, incitement, sedition, etc.