This may be country dependent. In the US, the Supreme Court has been clear that there is no hate speech limitation to the 1st amendment, for example. But there are limits to lying, as in perjury and libel cases.

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.