Threats will also be legal. This after all is just a series of noises. To be consistent a libertarian must claim that only a physical violation is illegal. A rapist who threatens his victim with a knife will not be convicted in court unless he physically hurts his victim because he will claim that the knife is his and he was taking it for a walk. Sure, he uttered a few words about killing the poor woman if she did not obey him, but they were just sounds and it is her own fault if she interpreted those noises as threatening.
I'm not getting the connection between IP and facts. For example, nobody has IP over gravity; how could anyone assume it exists, then? We can't assume Newton invented gravity, but moreso, came up with the concept of gravity. Although this discovery is attributed to him, what is and what isn't can't be held under copyright law, and nobody's paying Newton's ancestors grand sums of money to mutter the concept of gravitational force.
So let's say someone witnessed the man mentioning that he was going to kill a woman with a knife, with a knife in hand. Now, the to-be assailant may not own IP over "I'm gonna kill you and then I'm gonna rape you" (as has been said numerous times I'm certain,) he can still be attributed to having repeated those words, by both the victim and a witness. If we can then assume the man did, in fact, say those words, and was caught with a knife, if that society specifically disallows threats to kill, he would be taken care of however they take care of men such as that.
The point is, the man did not invent the phrase "I'm gonna kill you and then I'm gonna rape you," but that doesn't mean he still can't use it to get his intent across.
Likewise, when it comes to novels, every writer ever has said the following: "I love you"/"He loves me"/"I think I love you"/"I think I'm in love with you" etc., so who owns the IP over these strings of words? Nobody; so now we must figure out where to draw the line when it comes to how long a string should be before we can say it is intellectual property. However, because there would be no national government to come to an agreement on this matter (per libertarian ideals), and no national government to enforce it even if society came to a consensus at some point in time, there would be no way to enforce copyright. No writer invented the concept of love. A writer is only going to string together events in a timeline, or concepts he's realized based on concepts realized by others. If a scientist figures out gravity is much more than Newton ever realized, does he then own the IP of gravity? And if another scientist took that scientist's ideas, and expanded on them, and improved him, does that scientist now owe royalties? It's a trivial matter, and anyone can say, "Well I came up with it first."