Libel/slander laws do not limit speech. They can only be applied after the fact. So you can be held responsible for what you say or write, but you cannot be restrained from saying it in the first place.
This doesn't make sense. Laws forbid you to utter slanderous statements. Other laws forbid you to utter "fire" in a theatre. In both cases, I can commit the offense. So either slander laws *do* limit speech or the "don't shout fire in a theatre" does *not* limit free speech. Which is it?