Your line of argument is a commonly used one with regard to free speech, rigby, and I am sure it's one that many people agree with. What makes it not conclusive for me is that social mores change and things that in the past could not be said according to your rules can now be said, quite rightly. In science, for instance, things that were regarded as blasphemous and wicked at one time, because of the stranglehold religion and the law had on people's freedom of speech, are now common knowledge and banning utterances about them would be ridiculous as well as wrong.
All of which is just a diversion, a related diversion, from what KH said and the judgement that she must pay the costs. I don't know the whole story but if what she said damaged Jack Monroe's reputation, which is what's being said, then obviously, law or no law, what she did was wrong and it's right that she's having to pay for it.