While realistically such consensus is required in some cases anyway due to the imprecise nature of lawmaking, we should still strive for clear ruleset as a baseline, precisely so that the little guy is as informed of his rights as he reasonably can be.
And it doesn't need go very far. Inciting violence, threats to ones well being or insults towards a group, spoken to a crowd, say 10+ people, either verbally, or written, or gestured. That would include any medium which assumed an audience of more then 10 people. Yes, I'd include online forums, tweets, etc in that.
Like, I can't think of any socially relevent commentary that needs you say things of that sort, unless its because you're basically rebuting against someone else doing the same. And again, don't need to jail people, a fine would be a good start.
You can even express very inappropriate ideas without resorting to these. For example: "If X were truly less intelligent, it could be that this alone would explain why they are poorer overall, and so, no amount of extra care would help, because their intelligence is an innate limitation." No insults, no threats, no violence. Yet still incredibly controversial. Now the people you'd say this to might be tempted to insult you back, but if they did, they'd be fined, so instead they'd also have to be civil. For example: "That's true, but there's no proof that X are innately less intelligent, and there's known examples of Xs which have demonstrated higher then average intelligence, so its a moot argument, and one that seems to imply a certain innate bias against X from Y. If it were true, and this shows it, that Y had an innate racism against X, then its possible Y wants to keep X poor."
Please prove me otherwise, but I don't see what's so hard about enforcing some civility in speech when expressed to a sizable audience.
Maybe, but probably more likely we'll just end up where media and public discourse just becomes slightly more civil, tones down insults and focueses a little more on substance to make its claims.
I similarly don't have a way to prove this would be the outcome, I admit. I rely on a different premise, that we're a reasonable democracy, and that just as we work to fight collusion and corruption, we'd manage to control abuse of such laws in cases where they'd be used to oppress and control in a non democratic way. I feel if you don't believe our society can do this, then we're doomed to lose our freedoms to an authoritative regime anyways.