Tim Soutphommasane discusses the Australian federal government's proposed human rights and anti-discrimination bill, and says:
We may have free speech, but it has its legal limits. Most of us would say it has its moral limits too.
It's a remark made only in passing, but I think it's worth noting that the apparent symmetry of legal limits (which, Tim's right, there are) and moral limits (which there are too) could be misleading.
Legal limits to free speech are real limits; they restrain people from saying certain things on pain of incurring clear penalties if they go ahead and do say them. Moral limits don't work in the same way. You might think, as I do, that there are moral reasons why people shouldn't engage in Holocaust denial. But our thinking this doesn't prevent anyone from actually doing so; nor, in my view, should they be prevented. People's moral views do, of course, have an influence on how others conduct themselves, including in speech; still, a moral influence is different from and (usually) weaker than a legal penalty. One shouldn't imagine - not that Tim himself does - that legal and moral limits are of a kind, or that it would be desirable for all moral limits on free speech (as judged anyway by whom?) to be translated into legal ones.