It's difficult to judge speech even by contemporary standards. There tend to be high bars for bad speech, clearly harmful, E.G. fire in a crowd when there isn't fire.

How easy is it to prove something is a lie, rather than a very selective viewpoint or opinion? What if someone chooses to believe a set of sources biased to their preferred outcome?

We should also be lucky to encounter and hopefully have laws against hate speech; the slippery slope stuff that's subjectively icky but not quite across that line is more insidious.