[fastball]

Those things require knowing that what you are saying is false – the damage is in deliberately trying to mislead people, not the source of the information.

That is obviously very different from saying "I don't like this person so we should limit their freedom of speech even though they're not deliberately misleading anyone".

The point is that you should be trying to establish policy that doesn't come back to bite you in the ass when the prevailing winds change. Saying that you're not allowed to say things that 1. you know aren't true and 2. damage others, is a fairly objective standard. "This guy is a felon so we should limit his speech, regardless of what he is saying" is not.

[jungletime]

https://en.wikipedia.org/wiki/Trial_of_Socrates

[burkaman]

This is a reasonable stance, and I believe that it makes sense in your head, but I promise that if you try to actually write a law, "aren't true" and "damage others" are basically impossible to define. You're gonna have to draw some arbitrary-seeming lines based on how you want society to look, and be open to moving the lines if there are unexpected consequences. You can't write a clean protocol definition of acceptable human communication.

Would you pass a law that makes all lying illegal? Why not? Does speech have to directly damage someone? Financially, emotionally, what? What threshold of damage is punishable? Couldn't one argue that promoting communism "damages others"? The Secretary of Defense announcing a fake foreign invasion should probably be illegal, but a random drunk person claiming "the Chinese are invading" probably shouldn't be. So there's a line somewhere between those two people, where is it?

[fastball]

Literally all of the things you mentioned except Child Pornography (which is more of a production issue than speech issue anyway) meet that standard. So we can clearly write laws about it. No, lying in general isn't limited. Lying that damages other people/things is, however.

It's only perjury if you knowingly lie, which (when under oath) damages the integrity of the justice system. It's only libel if you tell a deliberate falsehood and it damages someone else directly. etc.